CVE-2026-72435: netfilter: ipset: fix order of kfree_rcu() and rcu_assign_pointer()

In the Linux kernel, the following vulnerability has been resolved:

netfilter: ipset: fix order of kfreercu() and rcuassignpointer()

Sashiko pointed out that kfreercu() was called before rcuassignpointer() in handling the comment extension. Fix the order so that rcuassignpointer() called first.