Some DSA drivers may or may not support multiple software bridges on top
of an hardware switch.

It is more convenient for them to access the bridge's net_device for
finer configuration.

Removing the need to craft and access a bitmask also simplifies the
code.

This patch changes the signature of bridge related functions, update DSA
drivers, and removes dsa_slave_br_port_mask.
Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Tested-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>