realtimer_expire: avoid proc lock recursion when called from itimer_proc_continue()

[kib]

Summary

It is fine to drop the process lock there, process cannot exit until its timers are cleared.

[kib]

Upload the correct version of the patch.
PHOLD() there is not needed and is even wrong.

[markj]

I believe there is a similar recursion with kqueue timers: kqtimer_proc_continue() holds the proc lock, and filt_timerexpire() may attempt to acquire it.

[kib]

Handle recursion in filter_timerexpire()