vxlan: fix missing options_len update on RX with collect metadata

When signalling to metadata consumers that the metadata_dst entry
carries additional GBP extension data for vxlan (TUNNEL_VXLAN_OPT),
the dst's vxlan_metadata information is populated, but options_len
is left to zero. F.e. in ovs, ovs_flow_key_extract() checks for
options_len before extracting the data through ip_tunnel_info_opts_get().

Geneve uses ip_tunnel_info_opts_set() helper in receive path, which
sets options_len internally, vxlan however uses ip_tunnel_info_opts(),
so when filling vxlan_metadata, we do need to update options_len.

Fixes: 4c222798 ("ip-tunnel: Use API to access tunnel metadata options.")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/vxlan.c

@@ -1308,8 +1308,10 @@ static int vxlan_udp_encap_recv(struct sock *sk, struct sk_buff *skb)
 		gbp = (struct vxlanhdr_gbp *)vxh;
 		md->gbp = ntohs(gbp->policy_id);
 
-		if (tun_dst)
+		if (tun_dst) {
 			tun_dst->u.tun_info.key.tun_flags |= TUNNEL_VXLAN_OPT;
+			tun_dst->u.tun_info.options_len = sizeof(*md);
+		}
 
 		if (gbp->dont_learn)
 			md->gbp |= VXLAN_GBP_DONT_LEARN;