Massively blow up the locking-related KASSERTs used to make sure
that we end up in a consistent locking state at the end of
udp_output() in order to be able to see what the values are based
on which we once took a decision (note: some values may have changed).

This helped to debug a syzkaller report.

MFC after: 2 months
Event: Waterloo Hackathon 2019