Accept additional T.38 reinvites after an initial one has been handled.

Discussion of this subject has yielded that it is not actually acceptable to change
T.38 parameters after the initial reinvite but declining is harsh and can cause the
fax to fail when it may be possible to allow it to continue. This patch changes things
so that additional T.38 reinvites are accepted but parameter changes ignored. This gives
the fax a fighting chance.

(closes issue #15610)
Reported by: huangtx2009


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@210817 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -8463,6 +8463,7 @@ static int process_sdp(struct sip_pvt *p, struct sip_request *req, int t38action
 	}
 	
 	if (udptlportno != -1) {
+		if (p->t38.state != T38_ENABLED) {
 			int found = 0, x;
 		
 			old = 0;
@@ -8566,6 +8567,7 @@ static int process_sdp(struct sip_pvt *p, struct sip_request *req, int t38action
 				   p->owner && p->lastinvite) {
 				change_t38_state(p, T38_PEER_REINVITE); /* T38 Offered in re-invite from remote party */
 			}
+		}
 	} else {
 		change_t38_state(p, T38_DISABLED);
 	}