Retire the F_KERNEL flag, it got superseded by route priority and RTP_MINE.

Retire the F_KERNEL flag, it got superseded by route priority and RTP_MINE.

Only problem is when route(8) is used to modify/delete a bgpd owned route.
Exact behaviour for that is still a bit unclear but F_KERNEL does not help
in this case either. In the kr_fib_delete/change remove F_BGPD_INSERTED
in that case as a first step.
OK tb@