Revert "socket: if we fail to create an instantiated service for a socket, don't put the socket in failure mode"

This reverts commit 9586cdfab6.
(but not the TODO hunk).

The bug was already fixed by 1a710b43. And if other errors occur, we
don't want to leave the socket active in order to avoid having socket
tarpits.

src/socket.c

@@ -1494,6 +1494,7 @@ static void socket_enter_running(Socket *s, int cfd) {
 
 fail:
         log_warning("%s failed to queue socket startup job: %s", UNIT(s)->id, bus_error(&error, r));
+        socket_enter_stop_pre(s, SOCKET_FAILURE_RESOURCES);
 
         if (cfd >= 0)
                 close_nointr_nofail(cfd);