netfilter: nf_tables: Compare netdev hooks based on stored name

The 1:1 relationship between nft_hook and nf_hook_ops is about to break,
so choose the stored ifname to uniquely identify hooks.

Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>