Revert "ipfilter: Avoid stopping with a lock held"

The timeout function still tries to acquire the rwlock, and now it
deadlocks, since the callout framework will have already acquired it.

This reverts commit 1fa6daaafd74c1a457dcfe26e0a5943b5441dc9d.

PR: 282478
Reported by: markj
Approved by: emaste (mentor)