Move invoking of callout_stop(&lle->lle_timer) into llentry_free().

This deduplicates the code a bit, and also implicitly adds missing
callout_stop() to in[6]_lltable_delete_entry() functions.

PR: 209682, 225927
Submitted by: hselasky (previous version)
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D4605