netfilter: nf_tables: handle meta/lookup with direct call

Currently nft uses inlined variants for common operations
such as 'ip saddr 1.2.3.4' instead of an indirect call.

Also handle meta get operations and lookups without indirect call,
both are builtin.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>