urlprotocol: receive a list of protocols from the caller

This way, the decisions about which protocols are available for use in
any given situations can be delegated to the caller.

libavformat/rtmphttp.c

@@ -208,7 +208,7 @@ static int rtmp_http_open(URLContext *h, const char *uri, int flags)
     }
 
     /* alloc the http context */
-    if ((ret = ffurl_alloc(&rt->stream, url, AVIO_FLAG_READ_WRITE, NULL)) < 0)
+    if ((ret = ffurl_alloc(&rt->stream, url, AVIO_FLAG_READ_WRITE, NULL, h->protocols)) < 0)
         goto fail;
 
     /* set options */