Synopsis:
nmcli connection clone [--temporary] [id|uuid|path] <ID> <new name>

It copies the <ID> connection as <new name>. The command is very useful
if there is a connection, but another one is needed for a related
configuration. One can copy the existing profile and modify it for the
new situation.

For example:
$ nmcli con clone main-eth second-eth
$ nmcli con mod second-eth connection.interface-name em4

Fixes: 721e917cb6c3f6bea7e856aaed0cd49626887db1

https://bugzilla.gnome.org/show_bug.cgi?id=755995

This allows the ipv4.dhcp-timeout default value to be set from user
configuration.

https://bugzilla.gnome.org/show_bug.cgi?id=756423

Add the 'lldp' property to NMSettingConnection, which specifies
whether the reception and parsing of LLDP frames to discover neighbor
devices should be enabled.

No longer support disabling the global-dns configuration via the
"enable" option.

Instead, the user can put the entire dns-configuration in one separate
snippet, and disable it altogether with ".config.enable".

Support a new configuration option

  [.config]
  enable=<ENABLED>

for configuration snippets.

This new [.config] section is only relevant within the snippet itself
and it is not merged into the combined configuration.

Currently only the "enable" key is supported. If the "enable" key is
missing, it obviously defaults to being enabled. It allows snippets
to be skipped from loading. The main configuration "NetworkManager.conf"
cannot be skipped.

<ENABLED> can be a boolean value (false), to skip a configuration
snippet from loading.
It can also be a string to match against the NetworkManager version,
like "enable=nm-version-min:1.1,nm-version-min:1.0.6"

There are several motivations for this:

- the user can disable an entire configuration snippet by toggeling
  one entry.
  This generalizes  the functionality of the global-dns.enable
  setting, but in a way that applies to configuration on a per-file
  basis.

- for developing, we often switch between different versions of
  NetworkManager. Thus, we might want to use different configuration.
  E.g. before global-dns options, I want to use "dns=none" and manage
  resolv.conf myself. Now, I can use global-dns setting to do that.
  That can be achieved with something like the following (not exactly,
  it's an example only):

      [.config]
      enable=nm-version-min:1.1
      [main]
      dns=default
      [global-dns-domain-*]
      nameserver=127.0.0.1

  Arguably, this would be more awesome, if we would bump our micro devel
  version (1.1.0) more often while developing 1.2.0 (*hint*).

- in principle, packages could drop configuration snippets and enable
  them based on the NetworkManager version.

- with the "env:" spec, you can enable/disable snippets by configuring
  an environment variable. Again, useful for testing and developing.