audiohooks: Reevaluate the bridge technology when an audiohook is added or removed.

Adding a mixmonitor to a channel causes the bridge to change technologies
from native to simple_bridge so the call can be recorded.  However, when
the mixmonitor is stopped the bridge does not switch back to the native
technology.

* Added unbridge requests to reevaluate the bridge when a channel
audiohook is removed.

* Moved the unbridge request into ast_audiohook_attach() ensure that the
bridge reevaluates whenever an audiohook is attached.  This simplified the
mixmonitor and chan_spy start code as well.

* Added defensive code to stop_mixmonitor_full() in case additional
arguments are ever added to the StopMixMonitor application.

* Made ast_framehook_detach() not do an unbridge request if the framehook
does not exist.

* Made ast_framehook_list_fixup() do an unbridge request if there are any
framehooks.  Also simplified the loop.

ASTERISK-24195 #close
Reported by: Jonathan Rose

Review: https://reviewboard.asterisk.org/r/4046/
........

Merged revisions 424506 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/13@424507 f38db490-d61c-443f-a65b-d21fe96a405b