channel_internal_api: Publish a snapshot change when linkedids change

Snapshots are now not published *quite* as much as they used to. One instance
where they are not published any longer is during bridge enter and exit - the
state of the channel doesn't change, the bridge does. However, channels are
changed when a linkedid is propagated; previously, the channel's state would
be updated and published during the bridge enter event. Now this must be
explicitly done.
........

Merged revisions 416300 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@416301 65c4cc65-6c06-0410-ace0-fbb531ad65f3