netfilter: nf_tables: Fix oversized kvmalloc() calls

The commit 7661809d ("mm: don't allow oversized kvmalloc() calls")
limits the max allocatable memory via kvmalloc() to MAX_INT.

Reported-by:  <syzbot+cd43695a64bcd21b8596@syzkaller.appspotmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>