NMRemoteSettings was looking for a signal handler on an
NMRemoteConnection using only G_SIGNAL_MATCH_FUNC, which means it
would get tripped up if a connection was known to two different
NMRemoteSettings objects at once. Although that can't happen now, it
might in the future if NMRemoteConnection became an NMObject, so use
G_SIGNAL_MATCH_DATA too.
