rocker: implement L2 bridge offloading

Add L2 bridge offloading support to rocker driver.  Here, the Linux bridge
driver is used to collect swdev ports into a tagged (or untagged) VLAN
bridge.  The switchdev will offload from the bridge driver the following L2
bridging functions:

 - Learning of neighbor MAC addresses on VLAN X  Learned mac/vlan is
installed in bridge FDB.  (And removed when device unlearns mac/vlan).
Learning must be turned off on each bridge port to disable the feature in
the bridge driver.

- Flooding of multicast/broadcast and unknown unicast pkts to (STP)
active ports in bridge.  The bridge driver is unaware of the flooding happening
at the device level.  Flooding must be turned off on each bridge port to
disable the feature on the bridge driver.

- STP port state is pushed down to driver/device.  The bridge still processes
STP BDPUs and maintains port STP state (for all VLANs in bridge), but
the driver/device must be notified of port STP state change to program
the device.

Multiple (VLAN) bridges are supported.  The device (implemented per
the OF-DPA spec) must use a portion of the VLAN namespace for
internal VLANs.  Right now, the upper 255 VLANs (0xf00 to 0xffe) are
used as internal VLAN IDs for untagged traffic and are not available
as port VLANs.

The driver uses the following interfaces:

1. To track VLAN add/del on ports in bridge:

.ndo_vlan_rx_add_vid
.ndo_vlan_rx_kill_vid

2. To track port add/del membership in bridge:

NETDEV_CHANGEUPPER netdevice notifier

3. To catch static FDB entries installed on bridge/vlan by user using netlink:

.ndo_fdb_add
.ndo_fdb_del

4. To be notified on port STP state change:

.ndo_switch_port_stp_update

5. To notify bridge driver on learned/forgotten mac/vlans on bridge port:

br_fdb_external_learn_add
br_fdb_external_learn_del
Signed-off-by: NScott Feldman <sfeldma@gmail.com>
Signed-off-by: NJiri Pirko <jiri@resnulli.us>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>