rtnetlink: handle rtnl_link netlink notifications manually

In order to support specifying device flags during device creation,
we must be able to roll back device registration in case setting the
flags fails without sending any notifications related to the device
to userspace.

This patch changes rollback_registered_many() and register_netdevice()
to manually send netlink notifications for devices not handled by
rtnl_link and allows to defer notifications for devices handled by
rtnl_link until setup is complete.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>