network: DHCP server Add support to transmit SIP server

1. DHCP server trasmit
2. Client parses and saves in leases
Implements http://www.rfc-editor.org/rfc/rfc3361.txt

```
Frame 134: 348 bytes on wire (2784 bits), 348 bytes captured (2784 bits) on interface 0
Ethernet II, Src: 42:65:85:d6:4e:32 (42:65:85:d6:4e:32), Dst: 1e:04:f8:b8:2f:d4 (1e:04:f8:b8:2f:d4)
Internet Protocol Version 4, Src: 192.168.5.1, Dst: 192.168.5.11
User Datagram Protocol, Src Port: 67, Dst Port: 68
Dynamic Host Configuration Protocol (ACK)
    Message type: Boot Reply (2)
    Hardware type: Ethernet (0x01)
    Hardware address length: 6
    Hops: 0
    Transaction ID: 0x7cc87cb4
    Seconds elapsed: 0
    Bootp flags: 0x0000 (Unicast)
    Client IP address: 0.0.0.0
    Your (client) IP address: 192.168.5.11
    Next server IP address: 0.0.0.0
    Relay agent IP address: 0.0.0.0
    Client MAC address: 1e:04:f8:b8:2f:d4 (1e:04:f8:b8:2f:d4)
    Client hardware address padding: 00000000000000000000
    Server host name not given
    Boot file name not given
    Magic cookie: DHCP
    Option: (53) DHCP Message Type (ACK)
        Length: 1
        DHCP: ACK (5)
    Option: (51) IP Address Lease Time
        Length: 4
        IP Address Lease Time: (3600s) 1 hour
    Option: (1) Subnet Mask (255.255.255.0)
        Length: 4
        Subnet Mask: 255.255.255.0
    Option: (3) Router
        Length: 4
        Router: 192.168.5.1
    Option: (6) Domain Name Server
        Length: 4
        Domain Name Server: 192.168.5.1
    Option: (42) Network Time Protocol Servers
        Length: 4
        Network Time Protocol Server: 192.168.1.1
    Option: (120) SIP Servers <=====here
        Length: 9
        SIP Server Encoding: IPv4 Address (1)
        SIP Server Address: 192.168.1.1
        SIP Server Address: 192.168.5.2
    Option: (101) TCode
        Length: 13
        TZ TCode: Europe/Berlin
    Option: (54) DHCP Server Identifier (192.168.5.1)
        Length: 4
        DHCP Server Identifier: 192.168.5.1
    Option: (255) End
        Option End: 255
```

```
cat /run/systemd/netif/state                                                                                                   ✔  ⚡  3148  16:40:51
OPER_STATE=routable
CARRIER_STATE=carrier
ADDRESS_STATE=routable
DNS=192.168.94.2 192.168.5.1
NTP=192.168.5.1
SIP=192.168.1.1 192.168.5.2

```

aa

4 files changed, 8 insertions, 2 deletions

diff --git a/src/systemd/sd-dhcp-client.h b/src/systemd/sd-dhcp-client.h
index ab62368e9c..46209cda05 100644
--- a/src/systemd/sd-dhcp-client.h
+++ b/src/systemd/sd-dhcp-client.h
@@ -87,6 +87,7 @@ enum {
         SD_DHCP_OPTION_NEW_POSIX_TIMEZONE          = 100,
         SD_DHCP_OPTION_NEW_TZDB_TIMEZONE           = 101,
         SD_DHCP_OPTION_DOMAIN_SEARCH_LIST          = 119,
+        SD_DHCP_OPTION_SIP_SERVER                  = 120,
         SD_DHCP_OPTION_CLASSLESS_STATIC_ROUTE      = 121,
         SD_DHCP_OPTION_PRIVATE_BASE                = 224,
        /* Windows 10 option to send when Anonymize=true */
diff --git a/src/systemd/sd-dhcp-lease.h b/src/systemd/sd-dhcp-lease.h
index d299c79121..b80d607fea 100644
--- a/src/systemd/sd-dhcp-lease.h
+++ b/src/systemd/sd-dhcp-lease.h
@@ -44,6 +44,7 @@ int sd_dhcp_lease_get_next_server(sd_dhcp_lease *lease, struct in_addr *addr);
 int sd_dhcp_lease_get_server_identifier(sd_dhcp_lease *lease, struct in_addr *addr);
 int sd_dhcp_lease_get_dns(sd_dhcp_lease *lease, const struct in_addr **addr);
 int sd_dhcp_lease_get_ntp(sd_dhcp_lease *lease, const struct in_addr **addr);
+int sd_dhcp_lease_get_sip(sd_dhcp_lease *lease, const struct in_addr **addr);
 int sd_dhcp_lease_get_mtu(sd_dhcp_lease *lease, uint16_t *mtu);
 int sd_dhcp_lease_get_domainname(sd_dhcp_lease *lease, const char **domainname);
 int sd_dhcp_lease_get_search_domains(sd_dhcp_lease *lease, char ***domains);
diff --git a/src/systemd/sd-dhcp-server.h b/src/systemd/sd-dhcp-server.h
index 2d5125db2c..2252a4aa88 100644
--- a/src/systemd/sd-dhcp-server.h
+++ b/src/systemd/sd-dhcp-server.h
@@ -46,8 +46,9 @@ int sd_dhcp_server_stop(sd_dhcp_server *server);
 int sd_dhcp_server_configure_pool(sd_dhcp_server *server, struct in_addr *address, unsigned char prefixlen, uint32_t offset, uint32_t size);
 
 int sd_dhcp_server_set_timezone(sd_dhcp_server *server, const char *timezone);
-int sd_dhcp_server_set_dns(sd_dhcp_server *server, const struct in_addr ntp[], unsigned n);
-int sd_dhcp_server_set_ntp(sd_dhcp_server *server, const struct in_addr dns[], unsigned n);
+int sd_dhcp_server_set_dns(sd_dhcp_server *server, const struct in_addr dns[], unsigned n);
+int sd_dhcp_server_set_ntp(sd_dhcp_server *server, const struct in_addr ntp[], unsigned n);
+int sd_dhcp_server_set_sip(sd_dhcp_server *server, const struct in_addr sip[], unsigned n);
 int sd_dhcp_server_set_emit_router(sd_dhcp_server *server, int enabled);
 
 int sd_dhcp_server_set_max_lease_time(sd_dhcp_server *server, uint32_t t);
diff --git a/src/systemd/sd-network.h b/src/systemd/sd-network.h
index 1cf4c2ec9d..d0b432274c 100644
--- a/src/systemd/sd-network.h
+++ b/src/systemd/sd-network.h
@@ -160,6 +160,9 @@ int sd_network_link_get_search_domains(int ifindex, char ***domains);
 /* Get the route DNS domain names for a given link. */
 int sd_network_link_get_route_domains(int ifindex, char ***domains);
 
+/* Get the sip servers for a given link. */
+int sd_network_link_get_sip_servers(int ifindex, char ***sip);
+
 /* Get whether this link shall be used as 'default route' for DNS queries */
 int sd_network_link_get_dns_default_route(int ifindex);