netfilter: nf_tables: handle more than 8 * PAGE_SIZE set name allocations

We currently have a limit of 8 * PAGE_SIZE anonymous sets. Lift that limit
by continuing the scan if the entire page is exhausted.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>