From Michael Grant.

This is an incompatible change.

This avoids desynchronisation between Babel and the kernel.

Pointless, but clearer to me.

All IHUs were interpreted as wildcards, which caused incorrect link quality
estimation.  And I didn't notice until now!

It was completely broken, but compensated with another bug.  No kidding.

The -u flag is gone, update-interval defaults to five times the hello interval.