netfilter: nf_tables: allow large allocations for new sets

netfilter: nf_tables: allow large allocations for new sets

The new fixed size hashtable backend implementation may result in a
large array of buckets that would spew splats from mm. Update this code
to fall back on vmalloc in case the memory allocation order is too
costly.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>