Annotate some ordering-related issues in solisten() which are not yet

resolved by socket locking: in particular, that we test the connection
state at the socket layer without locking, request that the protocol
begin listening, and then set the listen state on the socket
non-atomically, resulting in a non-atomic cross-layer test-and-set.

sys/kern/uipc_socket.c

@@ -265,6 +265,11 @@ solisten(so, backlog, td)
 {
 	int s, error;
 
+	/*
+	 * XXXRW: Ordering issue here -- perhaps we need to set
+	 * SO_ACCEPTCONN before the call to pru_listen()?
+	 * XXXRW: General atomic test-and-set concerns here also.
+	 */
 	s = splnet();
 	if (so->so_state & (SS_ISCONNECTED | SS_ISCONNECTING |
 			    SS_ISDISCONNECTING)) {