channel: add read-only socket property
channel: add read-only socket property

Channel users (such as spice widget) may want to know some connection
details. Instead of exposing various connection properties, we may as
well just have a GSocket property, with a strong warning on usage.

Signed-off-by: Marc-André Lureau <a6f2b960a4aca61381fc650a67901b2ac8e83e6d@redhat.com>
Acked-by: Victor Toso <39b7599ff73bbf5db531748ba5250f21fa7120ff@redhat.com>

flexVDI/spice-gtk,flexVDI/spice-gtk,fgouget/spice-gtk,fgouget/spice-gtk,fgouget/spice-gtk