MT#55283 support sendrecv subscribe req

Change-Id: I3a4905cea448017d21e6a59360b553e97ac6c6b6

daemon/call.c

@@ -4548,7 +4548,11 @@ static int monologue_subscribe_request1(struct call_media *src_media, struct cal
 		bf_copy(&dst_media->media_flags, MEDIA_FLAG_SEND, &src_media->media_flags, SP_FLAG_RECV);
 	else
 		MEDIA_CLEAR(dst_media, SEND);
-	MEDIA_CLEAR(dst_media, RECV);
+
+	if (flags->bidirectional)
+		bf_copy(&dst_media->media_flags, MEDIA_FLAG_RECV, &src_media->media_flags, SP_FLAG_SEND);
+	else
+		MEDIA_CLEAR(dst_media, RECV);
 
 	__rtcp_mux_set(flags, dst_media);
 	__generate_crypto(flags, dst_media, src_media);

docs/ng_control_protocol.md

@@ -1050,6 +1050,9 @@ Spaces in each string may be replaced by hyphens.
     For `publish` messages, support bidirectional media flow, i.e. don't
     respond with `recvonly` media but instead respond with `sendrecv`.
 
+    Similarly, for `subscribe request` messages, respond with `sendrecv`
+    instead of `sendonly`.
+
     For `connect` messages, in addition to `directional` sets up media flow in
     both directions.
 
@@ -2615,11 +2618,12 @@ subscription. This new call participant will be identified by a newly generated
 unique tag, or by the tag given in the `to-tag` key. If a label is to be set
 for the newly created subscription, it can be set through `set-label`.
 
-The reply message will contain a sendonly offer SDP in `sdp` which by default
-will mirror the SDP of the call participant being subscribed to. If multiple
-call participants are subscribed to at the same time, then this SDP will
-contain multiple media sections, combined out of the media sections of all
-selected call participants. This offer SDP can be manipulated with the same
+The reply message will contain a sendonly offer SDP (unless the flag
+`bidirectional` is given, in which case the SDP will be `sendrecv`) in `sdp`
+which by default will mirror the SDP of the call participant being subscribed
+to. If multiple call participants are subscribed to at the same time, then this
+SDP will contain multiple media sections, combined out of the media sections of
+all selected call participants. This offer SDP can be manipulated with the same
 flags as used in an `offer` message, including the option to manipulate the
 codecs. The reply message will also contain the `from-tags` (corresponding to
 the call participants being subscribed to) and the `to-tag` (corresponding to