i40e: add private flag to control source pruning

By default, our devices do source pruning, that is, they drop receive
packets that have the source MAC matching one of the receive filters.
Unfortunately, this breaks ARP monitoring in channel bonding, as the
bonding driver expects devices to receive ARPs containing their own
source address.

Add an ethtool private flag to control this feature.

Also, remove the netif_running() check when we process our private
flags. It's OK to reset when the device is closed and in most cases we
need the reset the apply these changes.

Signed-off-by: Mitch Williams <mitch.a.williams@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>