net/mlx5: Bridge, extract FDB delete notification to function

SWITCHDEV_FDB_DEL_TO_BRIDGE notification is generated in multiple places in
bridge code. Following patch in series changes the condition for the
notification. Extract the notification into dedicated helper function
mlx5_esw_bridge_fdb_del_notify() to only modify it in single place in the
future changes.

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>