zebra: Prevent a kernel route from being there when a connected should (backport #17088)

[mergify]

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.

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This is an automatic backport of pull request #17088 done by Mergify.

[mergify]

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	both modified:   zebra/connected.c

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[donaldsharp]

This change should only go in dev/10.2