net/mlx5e: Verify encapsulation is supported

When mlx5e_attach_encap() calls mlx5e_get_tc_tun() to get the tunnel
info data struct, check that returned value is not NULL, as would be in
the case of unsupported encapsulation.

Fixes: d386939a32 ("net/mlx5e: Rearrange tc tunnel code in a modular way")
Signed-off-by: Eli Cohen <eli@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>

drivers/net/ethernet/mellanox/mlx5/core/en_tc.c

@@ -2647,6 +2647,10 @@ static int mlx5e_attach_encap(struct mlx5e_priv *priv,
 	family = ip_tunnel_info_af(tun_info);
 	key.ip_tun_key = &tun_info->key;
 	key.tc_tunnel = mlx5e_get_tc_tun(mirred_dev);
+	if (!key.tc_tunnel) {
+		NL_SET_ERR_MSG_MOD(extack, "Unsupported tunnel");
+		return -EOPNOTSUPP;
+	}
 
 	hash_key = hash_encap_info(&key);