MT#11357 fix race condition during call teardown

Streams are removed from kernel forwarding at the "Final packet stats"
stage, which also stops the packet handler. But if a packet has already
been received at this point, with the packet handler already running,
only waiting to acquire the mutex, then the handler will run after the
streams have been removed from kernel and will promptly push them back
into kernel, where they will remain forever after.

daemon/call.c

@@ -566,6 +566,9 @@ static int stream_packet(struct streamrelay *sr_incoming, str *s, struct sockadd
 	m = c->callmaster;
 	smart_ntop_port(addr, fsin, sizeof(addr));
 
+	if (p_incoming->shutdown || p_outgoing->shutdown)
+		return 0;
+
 	if (sr_incoming->stun && is_stun(s)) {
 		stun_ret = stun(s, sr_incoming, fsin);
 		if (!stun_ret)
@@ -1800,6 +1803,7 @@ static void kill_callstream(struct callstream *s) {
 	for (i = 0; i < 2; i++) {
 		p = &s->peers[i];
 
+		p->shutdown = 1;
 		unkernelize(p);
 
 		for (j = 0; j < 2; j++) {

daemon/call.h

@@ -132,6 +132,7 @@ struct peer {
 	int			kernelized:1;
 	int			filled:1;
 	int			confirmed:1;
+	int			shutdown:1;
 };
 struct callstream {
 	struct obj		obj;