This changes the semantics of filters: RTPROT_BOOT will now be redistributed,
but only if it is explicitly mentioned in a redistribute filter.

Hopcount a kernel priority have nothing in common.

It still won't work, but will at least compile.
Reported by Mathias Mahnke.

From Michael Grant.

This is an incompatible change.

This avoids desynchronisation between Babel and the kernel.

Pointless, but clearer to me.