mgt: load vexts already in the manager

we foresaw this when we added VEXTs: while storage VEXTs have been happy with
loading in the worker process *), to support pluggable acceptors, VEXTs need to
be present in the manager for opening privileged ports etc.

*) There are two reasons why restricting VEXTs to the child worked for the
   (only?) existing storage VEXT: It does not insist on creating the storage
   file with elevated privileges, and, as far as VCL is concerned, the storage
   gets configured even if its code is not yet present (See STV_Config())

bin/varnishd/mgt/mgt_main.c

@@ -919,6 +919,9 @@ main(int argc, char * const *argv)
 	if (C_flag)
 		AZ(atexit(mgt_Cflag_atexit));
 
+	vext_copyin(vident);
+	vext_load();
+
 	/* If no -s argument specified, process default -s argument */
 	if (!arg_list_count("s"))
 		STV_Config(s_arg);
@@ -928,8 +931,6 @@ main(int argc, char * const *argv)
 
 	mgt_vcl_init();
 
-	vext_copyin(vident);
-
 	u = 0;
 	VTAILQ_FOREACH(alp, &arglist, list) {
 		if (!strcmp(alp->arg, "f") && alp->priv != NULL)