net: dsa: sync up switchdev objects and port attributes when joining the bridge

If we join an already-created bridge port, such as a bond master
interface, then we can miss the initial switchdev notifications emitted
by the bridge for this port, while it wasn't offloaded by anybody.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>