zebra: Fixup enable/disable of static routes in vrfs

zebra: Fixup enable/disable of static routes in vrfs

When a user enables and disables a vrf, we were not
properly cleaning up the static routes leaving us
in a state where we would crash by looking at anything
in zebra.

On disable of a vrf -> Search through all static routes
and if the nexthop vrf is the disabled vrf uninstall it.
Additionally uninstall all static routes in that zvrf

On enable of a vrf -> Search through all static routes
and if the nexthop vrf is the enabled vrf install it.
Additionally install all the static routes in that zvrf.

Ticket: CM-19768
Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>