net-sysfs: expose number of carrier on/off changes

This allows to monitor carrier on/off transitions and detect link
flapping issues:
 - new /sys/class/net/X/carrier_changes
 - new rtnetlink IFLA_CARRIER_CHANGES (getlink)

Tested:
  - grep . /sys/class/net/*/carrier_changes
    + ip link set dev X down/up
    + plug/unplug cable
  - updated iproute2: prints IFLA_CARRIER_CHANGES
  - iproute2 20121211-2 (debian): unchanged behavior

Signed-off-by: David Decotigny <decot@googlers.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/uapi/linux/if_link.h b/include/uapi/linux/if_link.h
index 16410b6e7819..9a7f7ace6649 100644
--- a/include/uapi/linux/if_link.h
+++ b/include/uapi/linux/if_link.h
@@ -144,6 +144,7 @@ enum {
         IFLA_NUM_RX_QUEUES,
         IFLA_CARRIER,
         IFLA_PHYS_PORT_ID,
+        IFLA_CARRIER_CHANGES,
         __IFLA_MAX
 };