Merge branch 'mctp-serial-minor-fixes'

Jeremy Kerr says:

====================
mctp serial minor fixes

We had a few minor fixes queued for a v4 of the original series, so
they're sent here as separate changes.

v2:
 - fix ordering of cancel_work vs. unregister_netdev.
====================

Link: https://lore.kernel.org/r/20211125060739.3023442-1-jk@codeconstruct.com.au
Signed-off-by: Jakub Kicinski <kuba@kernel.org>