dsa: Rename phys_port_mask to enabled_port_mask

The phys in phys_port_mask suggests this mask is about PHYs. In fact,
it means physical ports. Rename to enabled_port_mask, indicating
external enabled ports of the switch, which is hopefully less
confusing.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Tested-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>