netfilter: nft_payload: WARN_ON_ONCE instead of BUG

BUG() is too harsh for unknown payload base, use WARN_ON_ONCE() instead.
Signed-off-by: NPablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nft_payload.c

@@ -157,7 +157,8 @@ void nft_payload_eval(const struct nft_expr *expr,
 			goto err;
 		break;
 	default:
-		BUG();
+		WARN_ON_ONCE(1);
+		goto err;
 	}
 	offset += priv->offset;
 
@@ -664,7 +665,8 @@ static void nft_payload_set_eval(const struct nft_expr *expr,
 			goto err;
 		break;
 	default:
-		BUG();
+		WARN_ON_ONCE(1);
+		goto err;
 	}
 
 	csum_offset = offset + priv->csum_offset;