netfilter: nf_tables: fix module autoload with inet family

Use MODULE_ALIAS_NFT_EXPR() to make happy the inet family with nat.

Fixes: 63ce3940 ("netfilter: nft_redir: add inet support")
Fixes: 071657d2

 ("netfilter: nft_masq: add inet support")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>