netfilter: nf_tables: add .abort_skip_removal flag for set types

netfilter: nf_tables: add .abort_skip_removal flag for set types

The pipapo set backend is the only user of the .abort interface so far.
To speed up pipapo abort path, removals are skipped.

The follow up patch updates the rbtree to use to build an array of
ordered elements, then use binary search. This needs a new .abort
interface but, unlike pipapo, it also need to undo/remove elements.

Add a flag and use it from the pipapo set backend.

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