network: DHCPv6 client add support for prefix delegation hint

Add support for prefix hint lenth and prefix hint address
```
Frame 43: 177 bytes on wire (1416 bits), 177 bytes captured (1416 bits) on interface 0
Ethernet II, Src: f6:c1:08:4d:45:f1 (f6:c1:08:4d:45:f1), Dst: IPv6mcast_01:00:02 (33:33:00:01:00:02)
Internet Protocol Version 6, Src: fe80::d250:c82:7f6e:28d6, Dst: ff02::1:2
User Datagram Protocol, Src Port: 546, Dst Port: 547
DHCPv6
    Message type: Solicit (1)
    Transaction ID: 0x5c7902
    Rapid Commit
    Identity Association for Non-temporary Address
    Fully Qualified Domain Name
    Identity Association for Prefix Delegation
        Option: Identity Association for Prefix Delegation (25)
        Length: 41
        Value: 1b97b1690000000000000000001a0019ffffffffffffffff…
        IAID: 1b97b169
        T1: 0
        T2: 0
        IA Prefix
            Option: IA Prefix (26)
            Length: 25
            Value: ffffffffffffffff3c000000000000000000000000000000…
            Preferred lifetime: infinity
            Valid lifetime: infinity
            Prefix length: 60
            Prefix address: ::
    Option Request
    Client Identifier
    Elapsed time
```

1 files changed, 6 insertions, 0 deletions

diff --git a/src/network/networkd-dhcp6.c b/src/network/networkd-dhcp6.c
index e61eeda7d0..647623ac37 100644
--- a/src/network/networkd-dhcp6.c
+++ b/src/network/networkd-dhcp6.c
@@ -686,6 +686,12 @@ int dhcp6_configure(Link *link) {
                         return log_link_error_errno(link, r, "DHCP6 CLIENT: Failed to set prefix delegation: %m");
         }
 
+        if (link->network->dhcp6_pd_length > 0) {
+                r = sd_dhcp6_client_set_prefix_delegation_hint(client, link->network->dhcp6_pd_length, &link->network->dhcp6_pd_address);
+                if (r < 0)
+                        return log_link_error_errno(link, r, "DHCP6 CLIENT: Failed to set prefix hint: %m");
+        }
+
         link->dhcp6_client = TAKE_PTR(client);
 
         return 0;