netfilter: nft_tunnel: no need to call htons() when dumping ports

info->key.tp_src and tp_dst are __be16, when using nla_put_be16()
to dump them, htons() is not needed, so remove it in this patch.

Fixes: af308b94

 ("netfilter: nf_tables: add tunnel support")
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>