Add user-agent cache to GSSDP client

https://bugzilla.gnome.org/show_bug.cgi?id=653894
Fill user-agent cache from SSDP packets

https://bugzilla.gnome.org/show_bug.cgi?id=653894
Add ARP lookup for Linux

https://bugzilla.gnome.org/show_bug.cgi?id=653894