netfilter: nf_tables: Use stored ifname in netdev hook dumps

The stored ifname and ops.dev->name may deviate after creation due to
interface name changes. Prefer the more deterministic stored name in
dumps which also helps avoiding inadvertent changes to stored ruleset
dumps.

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