zebra: Push timer out if another route-map change comes in for zebra

zebra: Push timer out if another route-map change comes in for zebra

If we are running with a delayed timer to handle route-map changes
in zebra, if another route-map change is made to the cli, push
out the timer instead of not modifying the timer.  This will
allow a large set of route-maps to be possibly be read in by
the system and we don't have a state where new route-map
changes are being read in and having the timer pop in
the middle of it.

Additionally convert to use THREAD_OFF, preventing a possible
use after free as well as aligning the thread api usage
with what we consider correct.

Signed-off-by: Donald Sharp <sharpd@nvidia.com>