[core] quiet coverity warning

add arbitrary limit of 4096 fds to accept via systemd socket activation
(through environment variables)

src/network.c

@@ -529,7 +529,7 @@ static int network_socket_activation_from_env(server *srv, network_socket_config
     char *listen_fds = getenv("LISTEN_FDS");
     pid_t lpid = listen_pid ? (pid_t)strtoul(listen_pid,NULL,10) : 0;
     int nfds = listen_fds ? atoi(listen_fds) : 0;
-    int rc = (lpid == getpid() && nfds > 0)
+    int rc = (lpid == getpid() && nfds > 0 && nfds < 5000)
       ? network_socket_activation_nfds(srv, s, nfds)
       : 0;
     unsetenv("LISTEN_PID");