rc.d/ntpd: Restart ntpd when resuming from sleep.

ntpd does not always gracefully handle clock steps during resume.
This is probably most useful in conjunction with
ntpd_sync_on_start=YES which will work around any clock skew while
suspended.

Reviewed by: manu
Differential Revision: https://reviews.freebsd.org/D35479

(cherry picked from commit 1442fed7e25e9856464a0b0ce522ffc8cb473593)