i40e: don't remove netdev->dev_addr when syncing uc list

i40e: don't remove netdev->dev_addr when syncing uc list

In some circumstances, such as with bridging, it is possible that the
stack will add a devices own MAC address to its unicast address list.

If, later, the stack deletes this address, then the i40e driver will
receive a request to remove this address.

The driver stores its current MAC address as part of the MAC/VLAN hash
array, since it is convenient and matches exactly how the hardware
expects to be told which traffic to receive.

This causes a problem, since for more devices, the MAC address is stored
separately, and requests to delete a unicast address should not have the
ability to remove the filter for the MAC address.

Fix this by forcing a check on every address sync to ensure we do not
remove the device address.

There is a very narrow possibility of a race between .set_mac and
.set_rx_mode, if we don't change netdev->dev_addr before updating our
internal MAC list in .set_mac. This might be possible if .set_rx_mode is
going to remove MAC "XYZ" from the list, at the same time as .set_mac
changes our dev_addr to MAC "XYZ", we might possibly queue a delete,
then an add in .set_mac, then queue a delete in .set_rx_mode's
dev_uc_sync and then update netdev->dev_addr. We can avoid this by
moving the copy into dev_addr prior to the changes to the MAC filter
list.

A similar race on the other side does not cause problems, as if we're
changing our MAC form A to B, and we race with .set_rx_mode, it could
queue a delete from A, we'd update our address, and allow the delete.
This seems like a race, but in reality we're about to queue a delete of
A anyways, so it would not cause any issues.

A race in the initialization code is unlikely because the netdevice has
not yet been fully initialized and the stack should not be adding or
removing addresses yet.

Note that we don't (yet) need similar code for the VF driver because it
does not make use of __dev_uc_sync and __dev_mc_sync, but instead roles
its own method for handling updates to the MAC/VLAN list, which already
has code to protect against removal of the hardware address.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>