bridge: a netlink notification should be sent when those attributes are changed by ioctl

Now when we change the attributes of bridge or br_port by netlink,
a relevant netlink notification will be sent, but if we change them
by ioctl or sysfs, no notification will be sent.

We should ensure that whenever those attributes change internally or from
sysfs/ioctl, that a netlink notification is sent out to listeners.

Also, NetworkManager will use this in the future to listen for out-of-band
bridge master attribute updates and incorporate them into the runtime
configuration.

This patch is used for ioctl.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
Reviewed-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>