bonding: remove rtmsg_ifinfo called after bond_lower_state_changed

After the patch 'rtnetlink: bring NETDEV_CHANGELOWERSTATE event
process back to rtnetlink_event', bond_lower_state_changed would
generate NETDEV_CHANGEUPPER event which would send a notification
to userspace in rtnetlink_event.

There's no need to call rtmsg_ifinfo to send the notification
any more. So this patch is to remove it from these places after
bond_lower_state_changed.

Besides, after this, rtmsg_ifinfo is not needed to be exported.

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