Stop sending 183's after call hangup.

There where still cases where the 183 keep-alive mechanism would not stop
sending 183's even though the Asterisk server had sent a final reply to
the invite.

EDVX-28


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@234492 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -3785,6 +3785,7 @@ static int sip_hangup(struct ast_channel *ast)
 				}
 			} else {	/* Incoming call, not up */
 				const char *res;
+				AST_SCHED_DEL(sched, p->provisional_keepalive_sched_id);
 				if (p->hangupcause && (res = hangup_cause2sip(p->hangupcause)))
 					transmit_response_reliable(p, res, &p->initreq);
 				else