net/mlx5: Lag, properly lock eswitch if needed

Currently when doing hardware lag we check the eswitch mode
but as this isn't done under a lock the check isn't valid.

As the code needs to sync between two different devices an extra
care is needed.

- When going to change eswitch mode, if hardware lag is active destroy it.
- While changing eswitch modes block any hardware bond creation.
- Delay handling bonding events until there are no mode changes in
  progress.
- When attaching a new mdev to lag, block until there is no mode change
  in progress. In order for the mode change to finish the interface lock
  will have to be taken. Release the lock and sleep for 100ms to
  allow forward progress. As this is a very rare condition (can happen if
  the user unbinds and binds a PCI function while also changing eswitch
  mode of the other PCI function) it has no real world impact.

As taking multiple eswitch mode locks is now required lockdep will
complain about a possible deadlock. Register a key per eswitch to make
lockdep happy.

Signed-off-by: Mark Bloch <mbloch@nvidia.com>
Reviewed-by: Mark Zhang <markzhang@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>