Reduce number of timehands to just two. This is useful because
consumers can now be only one tc_windup() call late.

Use C99 initialization.

Tested by: pho (as part of the whole patch)
Reviewed by: jhb (same)
Discussed with: bde
Sponsored by: The FreeBSD Foundation
MFC after: 1 month
X-Differential revision: https://reviews.freebsd.org/D7302