CHANNEL(peer), chan_iax2, res_fax, SNMP agent: Fix deadlock from reaching across a bridge.

Calling ast_channel_bridge_peer() cannot be done while holding any channel
locks.  The reported issue hit the deadlock in chan_iax2, but an audit of
the ast_channel_bridge_peer() calls found three more locations where the
same deadlock can occur.

* Made CHANNEL(peer), res_fax, and the SNMP agent not call
ast_channel_bridge_peer() with any channel locked.  For CHANNEL(peer) I
had to rework the logic to not hold the channel lock.

* Made chan_iax2 no longer call ast_channel_bridge_peer().  It was done
for legacy reasons that no longer apply.

* Removed the iax.conf forcejitterbuffer option.  It is now always enabled
when the jitterbuffer option is enabled.  If you put a jitter buffer on a
channel it will be on the channel.

ASTERISK-24600 #close
Reported by: Jeff Collell

Review: https://reviewboard.asterisk.org/r/4342/
........

Merged revisions 430817 from http://svn.asterisk.org/svn/asterisk/branches/13


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@430819 65c4cc65-6c06-0410-ace0-fbb531ad65f3

configs/samples/iax.conf.sample

@@ -170,12 +170,6 @@ disallow=lpc10
 ; jitterbuffer=yes|no: global default as to whether you want
 ; the jitter buffer at all.
 ;
-; forcejitterbuffer=yes|no: in the ideal world, when we bridge VoIP channels
-; we don't want to do jitterbuffering on the switch, since the endpoints
-; can each handle this.  However, some endpoints may have poor jitterbuffers
-; themselves, so this option will force * to always jitterbuffer, even in this
-; case.
-;
 ; maxjitterbuffer: a maximum size for the jitter buffer.
 ; Setting a reasonable maximum here will prevent the call delay
 ; from rising to silly values in extreme situations; you'll hear
@@ -202,7 +196,6 @@ disallow=lpc10
 ;
 
 jitterbuffer=no
-forcejitterbuffer=no
 ;maxjitterbuffer=1000
 ;maxjitterinterps=10
 ;resyncthreshold=1000