net/mlx5: Bridge, add offload infrastructure

Create new files bridge.{c|h} in en/rep directory that implement bridge
interaction with representor netdevices and handle required
events/notifications, bridge.{c|h} in esw directory that implement all
necessary eswitch offloading infrastructure and works on vport/eswitch
level. Provide new kconfig MLX5_BRIDGE which is automatically selected when
both kernel bridge and mlx5 eswitch configs are enabled.

Provide basic infrastructure for bridge offloads:

- struct mlx5_esw_bridge_offloads - per-eswitch bridge offload structure
that encapsulates generic bridge-offloads data (notifier blocks, ingress
flow table/group, etc.) that is created/deleted on enable/disable eswitch
offloads.

- struct mlx5_esw_bridge - per-bridge structure that encapsulates
per-bridge data (reference counter, FDB, egress flow table/group, etc.)
that is created when first eswitch represetor is attached to new bridge and
deleted when last representor is removed from the bridge as a result of
NETDEV_CHANGEUPPER event.

The bridge tables are created with new priority FDB_BR_OFFLOAD in FDB
namespace. The new priority is between tc-miss and slow path priorities.
Priority consist of two levels: the ingress table that is global per
eswitch and matches incoming packets by src_mac/vid and redirects them to
next level (egress table) that is chosen according to ingress port bridge
membership and matches on dst_mac/vid in order to redirect packet to vport
according to the following diagram:

+
|
+---------v----------+
| |
| FDB_TC_OFFLOAD |
| |
+---------+----------+
|
|
+---------v----------+
| |
| FDB_FT_OFFLOAD |
| |
+---------+----------+
|
|
+---------v----------+
| |
| FDB_TC_MISS |
| |
+---------+----------+
|
+--------------------------------------+
| | |
| +------+ |
| | |
| +------v--------+ FDB_BR_OFFLOAD |
| | INGRESS_TABLE | |
| +------+---+----+ |
| | | match |
| | +---------+ |
| | | | +-------+
| | +-------v-------+ match | | |
| | | EGRESS_TABLE +------------> vport |
| | +-------+-------+ | | |
| | | | +-------+
| | miss | |
| +------+------+ |
| | |
+--------------------------------------+
|
|
+---------v----------+
| |
| FDB_SLOW_PATH |
| |
+---------+----------+
|
v

Signed-off-by: Vlad Buslov <vladbu@nvidia.com>
Reviewed-by: Jianbo Liu <jianbol@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>