kernel: mv88e6060: disable hardware level MAC learning

kernel: mv88e6060: disable hardware level MAC learning

Disable Marvell's hardware level MAC learning because it breaks station roaming.

When enabled it drops all frames that arrive from a MAC address
that is on a different port at learning table.

Problem description:
Multiple APs with inter-AP roaming connected to different ports,
when station moves from one AP on one port to another AP on another port,
traffic flow breaks down because the learning table is not updated.

Signed-off-by: Anderson Luiz Alves <alacn1@gmail.com>
[Replaced with upstream version, move to generic]
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>