TT#166107 fix stray ICE reset with rtcp-mux=require

Since we're creating a dummy sfd to hold the SRTCP context when we don't
have an actual RTCP port, we must make sure to remember and re-use this
dummy sfd during a re-invite. Otherwise we end up creating a duplicate
dummy sfd, which is detected as a different sfd and thus triggers an ICE
restart.

Change-Id: Iadc91e163bd15a3cd5f57656b52941724c920143

daemon/call.c

@@ -1029,6 +1029,8 @@ static void __assign_stream_fds(struct call_media *media, GQueue *intf_sfds) {
 			struct intf_list *il = l->data;
 
 			struct stream_fd *sfd = g_queue_peek_nth(&il->list, ps->component - 1);
+			if (!sfd)
+				sfd = ps->selected_sfd;
 			if (!sfd) {
 				// create a dummy sfd. needed to hold RTCP crypto context when
 				// RTCP-mux is in use

t/auto-daemon-tests.pl

@@ -1276,6 +1276,64 @@ is($ufrag_a, $ufrag_b, 'ufrag match');
 
 new_call;
 
+($port_a, $port_ax, $ufrag_a) = offer('ICE re-invite w rtcp-mux',
+	{ ICE => 'force', 'rtcp-mux' => ['require'] }, <<SDP);
+v=0
+o=- 1545997027 1 IN IP4 198.51.101.40
+s=tester
+t=0 0
+m=audio 16478 RTP/AVP 8
+c=IN IP4 198.51.100.1
+----------------------------------
+v=0
+o=- 1545997027 1 IN IP4 198.51.101.40
+s=tester
+t=0 0
+m=audio PORT RTP/AVP 8
+c=IN IP4 203.0.113.1
+a=rtpmap:8 PCMA/8000
+a=sendrecv
+a=rtcp:PORT
+a=rtcp-mux
+a=ice-ufrag:ICEUFRAG
+a=ice-pwd:ICEPWD
+a=candidate:ICEBASE 1 UDP 2130706431 203.0.113.1 PORT typ host
+a=candidate:ICEBASE 1 UDP 2130706175 2001:db8:4321::1 PORT typ host
+SDP
+
+is($port_a, $port_ax, 'port match');
+
+($port_b, $port_bx, $ufrag_b) = offer('ICE re-invite w rtcp-mux',
+	{ ICE => 'force', 'rtcp-mux' => ['require'] }, <<SDP);
+v=0
+o=- 1545997027 1 IN IP4 198.51.101.40
+s=tester
+t=0 0
+m=audio 16478 RTP/AVP 8
+c=IN IP4 198.51.100.1
+----------------------------------
+v=0
+o=- 1545997027 1 IN IP4 198.51.101.40
+s=tester
+t=0 0
+m=audio PORT RTP/AVP 8
+c=IN IP4 203.0.113.1
+a=rtpmap:8 PCMA/8000
+a=sendrecv
+a=rtcp:PORT
+a=rtcp-mux
+a=ice-ufrag:ICEUFRAG
+a=ice-pwd:ICEPWD
+a=candidate:ICEBASE 1 UDP 2130706431 203.0.113.1 PORT typ host
+a=candidate:ICEBASE 1 UDP 2130706175 2001:db8:4321::1 PORT typ host
+SDP
+
+is($port_b, $port_bx, 'port match');
+is($port_a, $port_b, 'port match');
+is($ufrag_a, $ufrag_b, 'ufrag match');
+
+new_call;
+
 ($port_a, undef, $ufrag_a) = offer('ICE re-invite',
 	{ ICE => 'force', flags => ['no port latching']}, <<SDP);
 v=0