tools: ynl: don't leak mcast_groups on init error

Make sure to free the already-parsed mcast_groups if
we don't get an ack from the kernel when reading family info.
This is part of the ynl_sock_create() error path, so we won't
get a call to ynl_sock_destroy() to free them later.

Fixes: 86878f14 ("tools: ynl: user space helpers")
Acked-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Link: https://lore.kernel.org/r/20240220161112.2735195-3-kuba@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

tools/net/ynl/lib/ynl.c

@@ -588,7 +588,13 @@ static int ynl_sock_read_family(struct ynl_sock *ys, const char *family_name)
 		return err;
 	}
 
-	return ynl_recv_ack(ys, err);
+	err = ynl_recv_ack(ys, err);
+	if (err < 0) {
+		free(ys->mcast_groups);
+		return err;
+	}
+
+	return 0;
 }
 
 struct ynl_sock *