netfilter: nft_tunnel: also dump ERSPAN_VERSION

This is not necessary, but it'll be easier to parse in userspace,
also given that other places like act_tunnel_key, cls_flower and
ip_tunnel_core are also doing so.
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nft_tunnel.c

@@ -479,6 +479,9 @@ static int nft_tunnel_opts_dump(struct sk_buff *skb,
 				 htonl(opts->u.vxlan.gbp)))
 			return -1;
 	} else if (opts->flags & TUNNEL_ERSPAN_OPT) {
+		if (nla_put_be32(skb, NFTA_TUNNEL_KEY_ERSPAN_VERSION,
+				 htonl(opts->u.erspan.version)))
+			return -1;
 		switch (opts->u.erspan.version) {
 		case ERSPAN_VERSION:
 			if (nla_put_be32(skb, NFTA_TUNNEL_KEY_ERSPAN_V1_INDEX,