net: switchdev: Replace port attr set SDO with a notification

Drop switchdev_ops.switchdev_port_attr_set. Drop the uses of this field
from all clients, which were migrated to use switchdev notification in
the previous patches.

Add a new function switchdev_port_attr_notify() that sends the switchdev
notifications SWITCHDEV_PORT_ATTR_SET and calls the blocking (process)
notifier chain.

We have one odd case within net/bridge/br_switchdev.c with the
SWITCHDEV_ATTR_ID_PORT_PRE_BRIDGE_FLAGS attribute identifier that
requires executing from atomic context, we deal with that one
specifically.

Drop __switchdev_port_attr_set() and update switchdev_port_attr_set()
likewise.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>