BUG/MINOR: mworker: mworker_kill should apply on every children

Commit 3f12887 ("MINOR: mworker: don't use children variable anymore")
introduced a regression.

The previous behavior was to send a signal to every children, whether or
not they are former children. Instead of this, we only send a signal to
the current children, so we don't try to kill -INT or -TERM all
processes during a reload.

No backport needed.
1 file changed