media-session: link all stream ports

Create a helper in the session manager to link all ports between
2 nodes.

Make the output endpoint call the input endpoint create_link, passing
the node or ports to link to.

Make the input endpoint complete the link by calling the session
helper to link all ports.

Remove the node policy, we're only using a policy for the endpoints
now.

src/modules/module-session-manager/client-endpoint.c

@@ -84,8 +84,8 @@ static int client_endpoint_stream_update(void *object,
 			PW_KEY_CLIENT_ID,
 			PW_KEY_ENDPOINT_ID,
 			PW_KEY_PRIORITY_SESSION,
-			PW_KEY_STREAM_NAME,
-			PW_KEY_STREAM_DESCRIPTION,
+			PW_KEY_ENDPOINT_STREAM_NAME,
+			PW_KEY_ENDPOINT_STREAM_DESCRIPTION,
 			NULL
 		};