net: dsa: Consistently use dsa_port for dsa_*_port_{apply, unapply}

We have all the information we need in dsa_port, so use it instead of
repeating the same arguments over and over again.

Suggested-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>