BFD: handle timing wheel prematurely firing events

BFD: handle timing wheel prematurely firing events

Improve handling of timeouts. Add a workaround for when timing wheel
fires an event a tiny amount of time before it should actually be
fired.  Don't delete unneeded events at all from timing wheel, instead
ignoring unexpected events. Enable the skipped BFD test, which passes
now.

Change-Id: I6ffd4fc0ba7a049ffe63bb0e5290641a7300dd6f
Signed-off-by: Klement Sekera <[email protected]>