zebra: Remove repeated enqueueing of system routes for rethinking

zebra: Remove repeated enqueueing of system routes for rethinking

The code as written before this code change point would enqueue
every system route type to be refigured when we have an
interface event.  I believe this was to originally handle bugs
in the way nexthop tracking was handled, mainly that if you keep
asking the question you'll eventually get the right answer.

Modify the code to not do this, we have fixed nexthop tracking
to not be so brain dead and to know when it needs to refigure
a route that it is tracking.

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