devlink: change port event netdev notifier from per-net to global

devlink: change port event netdev notifier from per-net to global

Currently only the network namespace of devlink instance is monitored
for port events. If netdev is moved to a different namespace and then
unregistered, NETDEV_PRE_UNINIT is missed which leads to trigger
following WARN_ON in devl_port_unregister().
WARN_ON(devlink_port->type != DEVLINK_PORT_TYPE_NOTSET);

Fix this by changing the netdev notifier from per-net to global so no
event is missed.

Fixes: 02a68a47eade ("net: devlink: track netdev with devlink_port assigned")
Signed-off-by: Jiri Pirko <[email protected]>
Reviewed-by: Jacob Keller <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Paolo Abeni <[email protected]>