don't just ignore but also strip invalid/unknown a=crypto

possibly fixes #207

Change-Id: I79df1b12ae7b335cd067be9238d76bf61cfb1536

daemon/sdp.c

@@ -190,6 +190,7 @@ struct sdp_attribute {
 		ATTR_FINGERPRINT,
 		ATTR_SETUP,
 		ATTR_RTPMAP,
+		ATTR_IGNORE,
 	} attr;
 
 	union {
@@ -520,8 +521,9 @@ static int parse_attribute_crypto(struct sdp_attribute *output) {
 	return 0;
 
 error:
-	ilog(LOG_ERROR, "Failed to parse a=crypto attribute: %s", err);
-	return -1;
+	ilog(LOG_ERROR, "Failed to parse a=crypto attribute, ignoring: %s", err);
+	output->attr = ATTR_IGNORE;
+	return 0;
 }
 
 static int parse_attribute_rtcp(struct sdp_attribute *output) {
@@ -1533,6 +1535,7 @@ static int process_session_attributes(struct sdp_chopper *chop, struct sdp_attri
 			case ATTR_SENDRECV:
 			case ATTR_FINGERPRINT:
 			case ATTR_SETUP:
+			case ATTR_IGNORE:
 				goto strip;
 
 			case ATTR_GROUP:
@@ -1596,10 +1599,12 @@ static int process_media_attributes(struct sdp_chopper *chop, struct sdp_media *
 			case ATTR_RTCP_MUX:
 				if (flags->ice_force_relay)
 					break;
+				// fall thru
 			case ATTR_INACTIVE:
 			case ATTR_SENDONLY:
 			case ATTR_RECVONLY:
 			case ATTR_SENDRECV:
+			case ATTR_IGNORE:
 				goto strip;
 
 			case ATTR_EXTMAP: