media-session: pass the client.id in the endpoint

Pass the client.id that we made this endpoint for in the endpoint
properties. This makes it possible to let pulse find the client
that belongs to the endpiont. The client.id is used to find the
client that actually made the object (the session manager)

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

@@ -306,6 +306,7 @@ int endpoint_init(struct endpoint *this,
 		PW_KEY_MEDIA_CLASS,
 		PW_KEY_PRIORITY_SESSION,
 		PW_KEY_ENDPOINT_NAME,
+		PW_KEY_ENDPOINT_CLIENT_ID,
 		PW_KEY_ENDPOINT_ICON_NAME,
 		NULL
 	};