TT#14008 fix kernel RTCP mux test

AVPF extended (non-compound) RTCP packets don't satisy the same RTP-like
header rules as regular RTCP compound packets, therefore we move the
RTCP mux test ahead of the RTP header parsing test.

Change-Id: Iecb3895d16796095f572c2eda2efa0a7a0dc69e7
(cherry picked from commit 4fa48df952)

kernel-module/xt_RTPENGINE.c

@@ -4034,10 +4034,15 @@ static inline int srtp_decrypt(struct re_crypto_context *c,
 	return c->cipher->decrypt(c, s, r, pkt_idx);
 }
 
-static inline int is_muxed_rtcp(struct rtp_parsed *r) {
-	if (r->header->m_pt < 194)
+static inline int is_muxed_rtcp(struct sk_buff *skb) {
+	// XXX shared code
+	unsigned char m_pt;
+	if (skb->len < 8) // minimum RTCP size
+		return 0;
+	m_pt = skb->data[1];
+	if (m_pt < 194)
 		return 0;
-	if (r->header->m_pt > 223)
+	if (m_pt > 223)
 		return 0;
 	return 1;
 }
@@ -4296,6 +4301,9 @@ src_check_ok:
 	if (!g->target.rtp)
 		goto not_rtp;
 
+	if (g->target.rtcp_mux && is_muxed_rtcp(skb))
+		goto skip1;
+
 	parse_rtp(&rtp, skb);
 	if (!rtp.ok) {
 		if (g->target.rtp_only)
@@ -4303,9 +4311,6 @@ src_check_ok:
 		goto not_rtp;
 	}
 
-	if (g->target.rtcp_mux && is_muxed_rtcp(&rtp))
-		goto skip1;
-
 	rtp_pt_idx = rtp_payload_type(rtp.header, &g->target);
 
 	// Pass to userspace if SSRC has changed.