chan_sip: SDP: Sidestep stream parsing when its media is disabled.

Previously, chan_sip parsed all known media streams in an SDP offer
like video (and text) even when videosupport=no (and textsupport=no).
This wasted processor power. Furthermore, chan_sip accepted SDP offers,
including no audio but just video (or text) streams although
videosupport=no (or textsupport=no). Finally, chan_sip denied the whole
offer instead of individual streams when they had encryption (SDES-sRTP)
unexpectedly enabled.

ASTERISK-29238
ASTERISK-29237
ASTERISK-29222

Change-Id: Ie49e4e2a11f0265f914b684738348ba8c0f89755

channels/chan_sip.c

@@ -10442,7 +10442,7 @@ static int process_sdp(struct sip_pvt *p, struct sip_request *req, int t38action
 		rtcp_mux_offered = has_media_level_attribute(iterator, req, "rtcp-mux");
 
 		/* Check for 'audio' media offer */
-		if (strncmp(m, "audio ", 6) == 0) {
+		if (p->rtp && strncmp(m, "audio ", 6) == 0) {
 			if ((sscanf(m, "audio %30u/%30u %17s %n", &x, &numberofports, protocol, &len) == 3 && len > 0) ||
 			    (sscanf(m, "audio %30u %17s %n", &x, protocol, &len) == 2 && len > 0)) {
 				codecs = m + len;
@@ -10552,7 +10552,7 @@ static int process_sdp(struct sip_pvt *p, struct sip_request *req, int t38action
 			}
 		}
 		/* Check for 'video' media offer */
-		else if (strncmp(m, "video ", 6) == 0) {
+		else if (p->vrtp && strncmp(m, "video ", 6) == 0) {
 			if ((sscanf(m, "video %30u/%30u %17s %n", &x, &numberofports, protocol, &len) == 3 && len > 0) ||
 			    (sscanf(m, "video %30u %17s %n", &x, protocol, &len) == 2 && len > 0)) {
 				codecs = m + len;
@@ -10631,7 +10631,7 @@ static int process_sdp(struct sip_pvt *p, struct sip_request *req, int t38action
 			}
 		}
 		/* Check for 'text' media offer */
-		else if (strncmp(m, "text ", 5) == 0) {
+		else if (p->trtp && strncmp(m, "text ", 5) == 0) {
 			if ((sscanf(m, "text %30u/%30u %17s %n", &x, &numberofports, protocol, &len) == 3 && len > 0) ||
 			    (sscanf(m, "text %30u %17s %n", &x, protocol, &len) == 2 && len > 0)) {
 				codecs = m + len;