zebra: Prevent a kernel route from being there when a connected should

zebra: Prevent a kernel route from being there when a connected should

There exists a series of events where a kernel route is learned
first( that happens to be exactly what a connected route should be )
and FRR ends up with both a kernel route and a connected route,
leaving us in a very strange spot.  This code change just mirrors
the existing code of if there is a connected route drop the kernel
route.  Here we just do the reverse, if we have a kernel route
already and a connected should be created, remove the kernel and
keep the connected.

Signed-off-by: Donald Sharp <sharpd@nvidia.com>
(cherry picked from commit 74e25198e74c4066b630515d2971c3c9381d70f2)