chan_pjsip: Fix deadlock when masquerading PJSIP channels.

Performing a directed call pickup resulted in a deadlock when PJSIP
channels were involved.

A masquerade needs to hold onto the channel locks while it swaps channel
information between the two channels involved in the masquerade.  With
PJSIP channels, the fixup routine needed to push a fixup task onto the
PJSIP channel's serializer.  Unfortunately, if the serializer was also
processing a task that needed to lock the channel, you get deadlock.

* Added a new control frame that is used to notify the channels that a
masquerade is about to start and when it has completed.

* Added the ability to query taskprocessors if the current thread is the
taskprocessor thread.

* Added the ability to suspend/unsuspend the PJSIP serializer thread so a
masquerade could fixup the PJSIP channel without using the serializer.

ASTERISK-24356 #close
Reported by: rmudgett

Review: https://reviewboard.asterisk.org/r/4034/
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Merged revisions 424471 from http://svn.asterisk.org/svn/asterisk/branches/12
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Merged revisions 424472 from http://svn.asterisk.org/svn/asterisk/branches/13


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@424473 65c4cc65-6c06-0410-ace0-fbb531ad65f3

funcs/func_frame_trace.c

@@ -334,6 +334,10 @@ static void print_frame(struct ast_frame *frame)
 		case AST_CONTROL_PVT_CAUSE_CODE:
 			ast_verbose("SubClass: PVT_CAUSE_CODE\n");
 			break;
+		case AST_CONTROL_MASQUERADE_NOTIFY:
+			/* Should never happen. */
+			ast_assert(0);
+			break;
 		case AST_CONTROL_STREAM_STOP:
 			ast_verbose("SubClass: STREAM_STOP\n");
 			break;