mlxbf_gige: stop interface during shutdown

SRU Justification:

[Impact]
The mlxbf_gige driver shutdown() is invoked during reboot
processing, but the stop() logic is not guaranteed to execute
on all distros. If stop() does not execute NAPI remains enabled
during system shutdown and can cause an exception if NAPI is
scheduled when interface is shutdown but not stopped.

[Fix]
The networking interface managed by the mlxbf_gige driver must
be stopped during reboot processing so that it is put into a
clean state and driver callbacks won't be called.

[Test Case]
* Put BF platform into a reboot loop
* Ensure that BF platform brings up "oob_net0" interface each reboot,
  and that no mlxbf_gige driver exceptions occur

[Regression Potential]
There is low potential for regression as this brings in upstream content.

[Other]
None