net/mlx5: Bridge, allow merged eswitch connectivity

Allow connectivity between representors of different eswitch instances that
are attached to same bridge when merged_eswitch capability is enabled. Add
ports of peer eswitch to bridge instance and mark them with
MLX5_ESW_BRIDGE_PORT_FLAG_PEER. Mark FDBs offloaded on peer ports with
MLX5_ESW_BRIDGE_FLAG_PEER flag. Such FDBs can only be aged out on their
local eswitch instance, which then sends SWITCHDEV_FDB_DEL_TO_BRIDGE event.
Listen to the event on mlx5 bridge implementation and delete peer FDBs in
event handler.

Signed-off-by: Vlad Buslov <vladbu@nvidia.com>
Reviewed-by: Roi Dayan <roid@nvidia.com>
Reviewed-by: Mark Bloch <mbloch@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>