Add AUTH_RULE_IDENTITY_LOOSE which allows to use IDr loosely as initiator

If it is set on an auth config IDr will not be sent, and later the configured
identity will not only be checked against the returned IDr, but also
against other identities contained in the responder's certificate.

src/libcharon/sa/ikev2/tasks/ike_auth.c

@@ -408,7 +408,8 @@ METHOD(task_t, build_i, status_t,
 		if (cfg)
 		{
 			idr = cfg->get(cfg, AUTH_RULE_IDENTITY);
-			if (idr && !idr->contains_wildcards(idr))
+			if (!cfg->get(cfg, AUTH_RULE_IDENTITY_LOOSE) && idr &&
+				!idr->contains_wildcards(idr))
 			{
 				this->ike_sa->set_other_id(this->ike_sa, idr->clone(idr));
 				id_payload = id_payload_create_from_identification(