netfilter: conntrack: clamp maximum hashtable size to INT_MAX

commit b541ba7d1f5a5b7b3e2e22dc9e40e18a7d6dbc13 upstream.

Use INT_MAX as maximum size for the conntrack hashtable. Otherwise, it
is possible to hit WARN_ON_ONCE in __kvmalloc_node_noprof() when
resizing hashtable because __GFP_NOWARN is unset. See:

  0708a0afe291 ("mm: Consider __GFP_NOWARN flag for oversized kvmalloc() calls")

Note: hashtable resize is only possible from init_netns.

Fixes: 9cc1c73ad666 ("netfilter: conntrack: avoid integer overflow when resizing")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Link: https://nvd.nist.gov/vuln/detail/CVE-2025-21648
[iwamatsu: Adjust context]
Signed-off-by: Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@toshiba.co.jp>