Prefer the realm of the user when doing referrals style ISC krb5-get-creds

The the realm of the user's principal and prefer that when doing a lookup.
This code still need to be smarter can cache the "initial value" -> positive result
to avoid roundtrips to the KDC.

lib/gssapi/krb5/init_sec_context.c

@@ -191,7 +191,7 @@ gsskrb5_get_creds(
     }
 
     ret = _gsskrb5_canon_name(minor_status, context, use_dns,
-			      target_name, &ctx->target);
+			      ctx->source, target_name, &ctx->target);
     if (ret)
 	return ret;