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.

This is an incompatible change in the syntax of the config file.

The protocol allows them to go up to 650 seconds, the value in msec
cannot be a short.

This is a throw-back to the Babel 0 (!) protocol.  There's no longer any
reason to treat self-updates specially.

It is seldom useful, and somewhat inconvenient.