rtnl: expose carrier value with possibility to set it

Signed-off-by: Jiri Pirko <jiri@resnulli.us>
Acked-by: Flavio Leitner <fbl@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/Documentation/networking/operstates.txt b/Documentation/networking/operstates.txt
index 1a77a3c..9769457 100644
--- a/Documentation/networking/operstates.txt
+++ b/Documentation/networking/operstates.txt
@@ -88,6 +88,10 @@
 packets. The name 'carrier' and the inversion are historical, think of
 it as lower layer.
 
+Note that for certain kind of soft-devices, which are not managing any
+real hardware, there is possible to set this bit from userpsace.
+One should use TVL IFLA_CARRIER to do so.
+
 netif_carrier_ok() can be used to query that bit.
 
 __LINK_STATE_DORMANT, maps to IFF_DORMANT: