chan_sip: Fix session timeout on retransmit of non-UDP packets

Change-Id I1cd33453c77c56c8e1394cd60a6f17bb61c1d957 Enable Session-Timers for
SIP over TCP (and TLS) also disables SIP retransmits in chan_sip for non-UDP
connections, allowing the TCP layer to handle the retransmits. Unfortunately,
this caused sessions to be terminated with a retransmit timeout becasue it
stopped at the point of the first retrans call.

This patch waits for the 64*T1 timer to expire instead.

ASTERISK-19968

Change-Id: I844f26801aada10bc94e9bebe6e151f0a8443204
(cherry picked from commit 98e42cc662)

channels/chan_sip.c

@@ -4243,7 +4243,10 @@ static enum sip_result __sip_reliable_xmit(struct sip_pvt *p, uint32_t seqno, in
 	pkt->retrans_stop_time = 64 * (pkt->timer_t1 ? pkt->timer_t1 : DEFAULT_TIMER_T1); /* time in ms after pkt->time_sent to stop retransmission */
 
 	if (!(p->socket.type & AST_TRANSPORT_UDP)) {
+		/* TCP does not need retransmits as that's built in, but with
+		 * retrans_stop set, we must give it the full timer_H treatment */
 		pkt->retrans_stop = 1;
+		siptimer_a = pkt->retrans_stop_time;
 	}
 
 	/* Schedule retransmission */