Fix previous make-network-process change

* src/process.c (Fmake_network_process): On 2018-07-09 "Explicitly
reject :server and :nowait (Bug#31903)", the sense of the SERVER check
was accidentally reversed so that we ended up looking for the wrong
ADDRESS.  Reported by T.V Raman in
<https://lists.gnu.org/archive/html/emacs-devel/2018-07/msg00437.html>.

src/process.c

@@ -3898,7 +3898,7 @@ usage: (make-network-process &rest ARGS)  */)
   CHECK_STRING (name);
 
   /* :local ADDRESS or :remote ADDRESS */
-  if (!NILP (server))
+  if (NILP (server))
     address = Fplist_get (contact, QCremote);
   else
     address = Fplist_get (contact, QClocal);