net: dsa: bcm_sf2: Disable learning while in WoL

When we are in Wake-on-LAN, we operate with the host sofware not running
a network stack, so we want to the switch to flood packets in order to
cause a system wake-up when matching specific filters (unicast or
multicast). This was not necessary before since we supported Magic
Packet which are targeting a broadcast MAC address which the switch
already floods.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>