net: dsa: bcm_sf2: Qualify phydev->dev_flags based on port

Similar to commit 92696286 ("net:
bcmgenet: Set phydev->dev_flags only for internal PHYs") we need to
qualify the phydev->dev_flags based on whether the port is connected to
an internal or external PHY otherwise we risk having a flags collision
with a completely different interpretation depending on the driver.

Fixes: aa9aef77

 ("net: dsa: bcm_sf2: communicate integrated PHY revision to PHY driver")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>