libteam needs this event notification in userspace when dev's master
dev has been changed. After this, the redundant notifications issue
would be fixed in the later patch 'rtnetlink: check DO_SETLINK_NOTIFY
correctly in do_setlink'.

Fixes: b6b36eb2 ("rtnetlink: Do not generate notifications for NETDEV_CHANGEUPPER event")
Signed-off-by: NXin Long <lucien.xin@gmail.com>
Acked-by: NDavid Ahern <dsahern@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>