netfilter: xt_hashlimit: replace vmalloc calls with kvmalloc

Replace vmalloc allocations with kvmalloc since
kvmalloc is more flexible in memory allocation

Signed-off-by: Denis Kirjanov <kirjanov@gmail.com>
Reviewed-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>