rtnl/do_setlink(): notify when a netdev is modified

Depending on which parameters were updated, the changes were not propagated via
the notifier chain and netlink.

The new flag has been set only when the change did not cause a call to the
notifier chain and/or to the netlink notification functions.

Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>