Merge branch 'net-ipa-add-a-driver-shutdown-callback'

Alex Elder says:

====================
net: ipa: add a driver shutdown callback

The final patch in this series adds a driver shutdown callback for
the IPA driver.  The patches leading up to that address some issues
encountered while ensuring that callback worked as expected:
  - The first just reports a little more information when channels
    or event rings are in unexpected states
  - The second patch recognizes a condition where an as-yet-unused
    channel does not require a reset during teardown
  - The third patch explicitly ignores a certain error condition,
    because it can't be avoided, and is harmless if it occurs
  - The fourth properly handles requests to retry a channel HALT
    request
  - The fifth makes a second attempt to stop modem activity during
    shutdown if it's busy

The shutdown callback is implemented by calling the existing remove
callback function (reporting if that returns an error).
====================

Link: https://lore.kernel.org/r/20201119224929.23819-1-elder@linaro.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>