client: Don't reserve multicast address in the client setting case

client: Don't reserve multicast address in the client setting case

When two multicast clients request specific transport
configurations, and "transport.client-settings" parameter is
set to true, it's wrong to actually require that these two
clients request the same multicast group.
Removed test_client_multicast_invalid_transport_specific test
cases as they wrongly require that the requested destination
address is supposed to be present in the address pool, also in
the case when "transport.client-settings" parameter is set to true.

Change-Id: I4580182ef35996caf644686d6139f72ec599c9fa

https://bugzilla.gnome.org/show_bug.cgi?id=793441