net/mlx5: Lag, Don't rescan if the device is going down

If MLX5_PRIV_FLAGS_DISABLE_ALL_ADEV is set it means the device is going
down and mlx5_rescan_drivers_locked() shouldn't be called.
With this patch and the previous one in the series, unbinding a PCI
function when its netdev is part of a bond works and leaves the system in a
working state.

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