netfilter: nft_set_rbtree: use binary search array in get command

netfilter: nft_set_rbtree: use binary search array in get command

Rework .get interface to use the binary search array, this needs a specific
lookup function to match on end intervals (<=). Packet path lookup is slight
different because match is on lesser value, not equal (ie. <).

After this patch, seqcount can be removed in a follow up patch.

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