MT#55283 Don't fail deleting the iptables chain if it is still in use

When base chain is "none", the admin is required to manage jumping into the
rtpengine chain. The chain can't be deleted if it is still referenced by
another rule, which is common in this configuration.

closes #1787

Change-Id: I8a72e1041a364db60870b5acececc234c8452bab

daemon/nftables.c

@@ -562,7 +562,7 @@ static const char *nftables_shutdown_family(struct mnl_socket *nl, int family, u
 
 	err = delete_chain(nl, family, seq, chain);
 	if (err) {
-		if (errno != ENOENT) // ignore trying to delete stuff that doesn't exist
+		if (errno != ENOENT && errno != EBUSY) // ignore trying to delete stuff that doesn't exist
 			return err;
 	}