e1000: Move cancel_work_sync to avoid deadlock

Previously, e1000_down called cancel_work_sync for the e1000 reset task
(via e1000_down_and_stop), which takes RTNL.

As reported by users and syzbot, a deadlock is possible in the following
scenario:

CPU 0:
  - RTNL is held
  - e1000_close
  - e1000_down
  - cancel_work_sync (cancel / wait for e1000_reset_task())

CPU 1:
  - process_one_work
  - e1000_reset_task
  - take RTNL

To remedy this, avoid calling cancel_work_sync from e1000_down
(e1000_reset_task does nothing if the device is down anyway). Instead,
call cancel_work_sync for e1000_reset_task when the device is being
removed.

Fixes: e400c744 ("e1000: Hold RTNL when e1000_down can be called")
Reported-by:  <syzbot+846bb38dc67fe62cc733@syzkaller.appspotmail.com>
Closes: https://lore.kernel.org/netdev/683837bf.a00a0220.52848.0003.GAE@google.com/


Reported-by: John <john.cs.hey@gmail.com>
Closes: https://lore.kernel.org/netdev/CAP=Rh=OEsn4y_2LvkO3UtDWurKcGPnZ_NPSXK=FbgygNXL37Sw@mail.gmail.com/


Signed-off-by: Joe Damato <jdamato@fastly.com>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Acked-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>