Revert "net/mlx4_en: Fix panic during reboot"

This reverts commit 9d2afba0.

The original issue would possibly exist if an external module
tried calling our "ethtool_ops" without checking if it still
exists.

The right way of solving it is by simply doing the check in
the caller side.
Currently, no action is required as there's no such use case.

Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>