mlxsw: spectrum: Centralize VLAN-aware bridge ref counting

mlxsw: spectrum: Centralize VLAN-aware bridge ref counting

We hold a reference count on the number of ports member in the
VLAN-aware bridge, as we only support one.

Instead of always incrementing / decrementing the reference count after
joining / leaving the bridge, simply do this accounting in the join /
leave functions.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>