kernel: Prevent unnecessary rfkill event generation.

Prevent unnecessary rfkill event generation when the state has
not actually changed. These events have to be delivered to
relevant userspace processes, causing these processes to wake
up and do something while they could as well have slept. This
obviously results in more CPU usage, longer time-to-sleep-again
and therefore higher power consumption.

Change-Id: I3ac4e141fbdf1315b74d3bad6aa96f34b00c3f92
CRs-fixed: 398283
Signed-off-by: Vitaly Wool <vitalywool@gmail.com>
Signed-off-by: Mykyta Iziumtsev <nikita.izyumtsev@gmail.com>
Signed-off-by: Deepthi Gowri <deepthi@codeaurora.org>