ipfilter: Don't reinitialize lock in timer function

[cy]

Summary

This is unnecessary and may result in a deadlock.

Fixes: 1fa6daaafd74

Test Plan

I will test on my firewall here at home.

[markj]

This is not sufficient to fix the referenced commit, it'll still deadlock after this change.

The problem is that callout_init_rw() causes the callout framework to acquire the rwlock before executing the timeout function, and that timeout function will try to acquire it again.