net: dsa: use new port type in helpers

Now that DSA exposes an enumerated type for the ports, we can use them
directly instead of checking bitmaps, which is more consistent.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>