net: dsa: dsa_slave_phy_connect(): extend phy's flags with port specific phy flags

The current get_phy_flags() is only processed when we connect to a PHY
via a designed phy-handle property via phylink_of_phy_connect(), but if
we fallback on the internal MDIO bus created by a switch and take the
dsa_slave_phy_connect() path then we would not be processing that flag
and using it at PHY connection time.

Suggested-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>