[zebra] do not touch socket before pidfile locking

Move zserv socket creation code into zebra_zserv_socket_init() and
call it only after pidfile lock has been acquired exclusively. This
keeps subsequent zebra daemons from deleting the working socket of
an already running process (bug #403).
diff --git a/zebra/zserv.c b/zebra/zserv.c
index a566e6d..cb5e411 100644
--- a/zebra/zserv.c
+++ b/zebra/zserv.c
@@ -1704,13 +1704,6 @@
   /* Client list init. */
   zebrad.client_list = list_new ();
 
-  /* Make zebra server socket. */
-#ifdef HAVE_TCP_ZEBRA
-  zebra_serv ();
-#else
-  zebra_serv_un (ZEBRA_SERV_PATH);
-#endif /* HAVE_TCP_ZEBRA */
-
   /* Install configuration write function. */
   install_node (&table_node, config_write_table);
   install_node (&forwarding_node, config_write_forwarding);
@@ -1737,3 +1730,14 @@
   /* Route-map */
   zebra_route_map_init ();
 }
+
+/* Make zebra server socket, wiping any existing one (see bug #403). */
+void
+zebra_zserv_socket_init (void)
+{
+#ifdef HAVE_TCP_ZEBRA
+  zebra_serv ();
+#else
+  zebra_serv_un (ZEBRA_SERV_PATH);
+#endif /* HAVE_TCP_ZEBRA */
+}