netfilter: idletimers - add send_nl_msg field

Send notifications when the label becomes active after an idle period.
Send netlink message notifications in addition to sysfs notifications.
Using a uevent with
      subsystem=xt_idletimer
      INTERFACE=...
      STATE={active,inactive}

This is backport from common android-3.0
commit: beb914e987cbbd368988d2b94a6661cb907c4d5a
with uevent support instead of a new netlink message type.

Cc: JP Abgrall <jpa@google.com>
Cc: Ashish Sharma <ashishsharma@google.com>
Cc: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>
Signed-off-by: Ashish Sharma <ashishsharma@google.com>
Signed-off-by: JP Abgrall <jpa@google.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: dmitry pervushin <dmitry.pervushin@linaro.org>