Clear the DTMF sending digit tracking on off nominal paths

In certain situations, when the RTP engine goes to send a DTMF end digit
it may be in a situation where the remote address is no longer available,
or the digit that was supposed to be sent is invalid. In such cases, we
need to clear the RTP counters appropriately. Otherwise, when the RTP
source is set again, we'll continue to think that we're in the middle of
sending a DTMF digit, which can confuse the remote party (signficantly).

(closes issue ASTERISK-21522)
Reported by: Corey Farrell
patches:
  rtp_dtmf_process_end.patch uploaded by Corey Farrell (License 5909)
........

Merged revisions 387213 from http://svn.asterisk.org/svn/asterisk/branches/1.8
........

Merged revisions 387216 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@387220 65c4cc65-6c06-0410-ace0-fbb531ad65f3

res/res_rtp_asterisk.c

@@ -2034,7 +2034,7 @@ static int ast_rtp_dtmf_end_with_duration(struct ast_rtp_instance *instance, cha
 {
 	struct ast_rtp *rtp = ast_rtp_instance_get_data(instance);
 	struct ast_sockaddr remote_address = { {0,} };
-	int hdrlen = 12, res = 0, i = 0;
+	int hdrlen = 12, res = -1, i = 0;
 	char data[256];
 	unsigned int *rtpheader = (unsigned int*)data;
 	unsigned int measured_samples;
@@ -2043,7 +2043,7 @@ static int ast_rtp_dtmf_end_with_duration(struct ast_rtp_instance *instance, cha
 
 	/* Make sure we know where the remote side is so we can send them the packet we construct */
 	if (ast_sockaddr_isnull(&remote_address)) {
-		return -1;
+		goto cleanup;
 	}
 
 	/* Convert the given digit to the one we are going to send */
@@ -2059,7 +2059,7 @@ static int ast_rtp_dtmf_end_with_duration(struct ast_rtp_instance *instance, cha
 		digit = digit - 'a' + 12;
 	} else {
 		ast_log(LOG_WARNING, "Don't know how to represent '%c'\n", digit);
-		return -1;
+		goto cleanup;
 	}
 
 	rtp->dtmfmute = ast_tvadd(ast_tvnow(), ast_tv(0, 500000));
@@ -2100,13 +2100,15 @@ static int ast_rtp_dtmf_end_with_duration(struct ast_rtp_instance *instance, cha
 
 		rtp->seqno++;
 	}
+	res = 0;
 
 	/* Oh and we can't forget to turn off the stuff that says we are sending DTMF */
 	rtp->lastts += rtp->send_duration;
+cleanup:
 	rtp->sending_digit = 0;
 	rtp->send_digit = 0;
 
-	return 0;
+	return res;
 }
 
 static int ast_rtp_dtmf_end(struct ast_rtp_instance *instance, char digit)