net/mlx5e: Fail safe mtu and lro setting

Use the new fail-safe channels switch mechanism to set new
netdev mtu and lro settings.

MTU and lro settings demand some HW configuration changes after new
channels are created and ready for action. In order to unify switch
channels routine for LRO and MTU changes, and maybe future configuration
features, we now pass to it a modify HW function pointer to be
invoked directly after old channels are de-activated and before new
channels are activated.

Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>