rtpengine: improve compatibility of rtpengine per call leg stats parsing

not all versions of rtpengine sends a key SSRC per stream.  For those that do not
the same information can be found in ingress SSRCs.  Add logic to check for the
SSRC value there if the SSRC key is not present.

(cherry picked from commit 992ee3df02148a940c255b8be7eb9d8e63465834)

src/modules/rtpengine/rtpengine.c

@@ -4490,7 +4490,8 @@ static void parse_call_stats_1(struct minmax_mos_label_stats *mmls,
 	long long ssrc;
 	char *endp;
 	bencode_item_t *ssrc_list, *ssrc_key, *ssrc_dict, *tags, *tag_key,
-			*tag_dict, *medias, *media, *streams, *stream;
+			*tag_dict, *medias, *media, *streams, *stream, *ingress_ssrcs,
+			*ingress_ssrc;
 	struct minmax_stats_vals min_vals = {.mos = 100}, max_vals = {.mos = -1},
 							 average_vals = {.avg_samples = 0}, vals_decoded;
 
@@ -4545,9 +4546,21 @@ static void parse_call_stats_1(struct minmax_mos_label_stats *mmls,
 					(char *)stream->child->iov[1].iov_base);
 			LM_DBG("rtpengine: XXX stream child val type %i\n",
 					stream->child->sibling->type);
-			if((ssrc = bencode_dictionary_get_integer(stream, "SSRC", -1))
-					== -1)
-				continue;
+			ssrc = bencode_dictionary_get_integer(stream, "SSRC", -1);
+			if(ssrc == -1) {
+				ingress_ssrcs = bencode_dictionary_get_expect(
+						stream, "ingress SSRCs", BENCODE_LIST);
+				if(!ingress_ssrcs || !ingress_ssrcs->child)
+					continue;
+				LM_DBG("rtpengine: XXX got ingress SSRCs\n");
+				ingress_ssrc = ingress_ssrcs->child;
+				if((ssrc = bencode_dictionary_get_integer(
+							ingress_ssrc, "SSRC", -1))
+						== -1) {
+					continue;
+				}
+			}
+
 			/* got a valid SSRC to watch for */
 			ssrcs[num_ssrcs] = ssrc;
 			LM_DBG("rtpengine: found SSRC '%lli' for label '%.*s'\n", ssrc,