net: dsa: use dsa_is_user_port everywhere

Most of the DSA code still check ds->enabled_port_mask directly to
inspect a given port type instead of using the provided dsa_is_user_port
helper. Change this.

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