rtmp: send check_bw as notification

Set the transactionId to 0 to signal the server a return _result/_error
is not expected.

Solves the problems experienced with strict rtmp servers.

libavformat/rtmp.h

@@ -32,6 +32,15 @@
 #define HMAC_IPAD_VAL 0x36
 #define HMAC_OPAD_VAL 0x5C
 
+/**
+ * A non-zero transaction id requires the server to send back
+ * a _result or _error response.
+ * Setting it to 0 marks the message as a notification not
+ * requiring feedback.
+ */
+
+#define RTMP_NOTIFICATION 0
+
 /**
  * emulated Flash client version - 9.0.124.2 on Linux
  * @{

libavformat/rtmpproto.c

@@ -573,7 +573,7 @@ static int gen_check_bw(URLContext *s, RTMPContext *rt)
 
     p = pkt.data;
     ff_amf_write_string(&p, "_checkbw");
-    ff_amf_write_number(&p, ++rt->nb_invokes);
+    ff_amf_write_number(&p, RTMP_NOTIFICATION);
     ff_amf_write_null(&p);
 
     ret = ff_rtmp_packet_write(rt->stream, &pkt, rt->chunk_size,