MT#15289 add "reset" flag to un-learn certain parameters

This enables switching over the endpoint of a dialogue to a new client
with potentially different capabilities

Change-Id: I973b3c5d004014cc73e6ebc3e87d03c742bc1951
(cherry picked from commit 69b7586aa4)

README.md

@@ -675,6 +675,17 @@ Optionally included keys are:
 		this opens a security hole and potentially allows RTP streams to be hijacked, either partly or
 		in whole.
 
+	- `reset`
+
+		This causes *rtpengine* to un-learn certain aspects of the RTP endpoints involved, such as
+		support for ICE or support for SRTP. For example, if `ICE=force` is given, then *rtpengine*
+		will initially offer ICE to the remote endpoint. However, if a subsequent answer from that
+		same endpoint indicates that it doesn't support ICE, then no more ICE offers will be made
+		towards that endpoint, even if `ICE=force` is still specified. With the `reset` flag given,
+		this aspect will be un-learned and *rtpengine* will again offer ICE to this endpoint.
+		This flag is valid only in an `offer` message and is useful when the call has been
+		transferred to a new endpoint without change of `From` or `To` tags.
+
 * `replace`
 
 	Similar to the `flags` list. Controls which parts of the SDP body should be rewritten.

daemon/call.c

@@ -2503,6 +2503,11 @@ int monologue_offer_answer(struct call_monologue *other_ml, GQueue *streams,
 		 * THIS side (recipient) before, then the structs will be populated with
 		 * details already. */
 
+		if (flags && flags->opmode == OP_OFFER && flags->reset) {
+			MEDIA_CLEAR(media, INITIALIZED);
+			MEDIA_CLEAR(other_media, INITIALIZED);
+		}
+
 		/* deduct protocol from stream parameters received */
 		if (other_media->protocol != sp->protocol) {
 			other_media->protocol = sp->protocol;

daemon/call_interfaces.c

@@ -552,6 +552,8 @@ static void call_ng_process_flags(struct sdp_ng_flags *out, bencode_item_t *inpu
 				out->strict_source = 1;
 			else if (!bencode_strcmp(it, "media-handover"))
 				out->media_handover = 1;
+			else if (!bencode_strcmp(it, "reset"))
+				out->reset = 1;
 			else if (it->iov[1].iov_len >= 5 && !memcmp(it->iov[1].iov_base, "SDES-", 5))
 				ng_sdes_option(out, it, 5);
 			else

daemon/sdp.h

@@ -33,6 +33,7 @@ struct sdp_ng_flags {
 	    strict_source:1,
 	    media_handover:1,
 	    dtls_passive:1,
+	    reset:1,
 	    dtls_off:1,
 	    sdes_off:1,
 	    sdes_unencrypted_srtp:1,