xfrm: SAD entries do not expire correctly after suspend-resume

  This fixes the following bug in the current implementation of
net/xfrm: SAD entries timeouts do not count the time spent by the machine 
in the suspended state. This leads to the connectivity problems because 
after resuming local machine thinks that the SAD entry is still valid, while 
it has already been expired on the remote server.

  The cause of this is very simple: the timeouts in the net/xfrm are bound to 
the old mod_timer() timers. This patch reassigns them to the
CLOCK_REALTIME hrtimer.

  I have been using this version of the patch for a few months on my
machines without any problems. Also run a few stress tests w/o any
issues.

  This version of the patch uses tasklet_hrtimer by Peter Zijlstra
(commit 9ba5f0).

  This patch is against 2.6.31.4. Please CC me.

Signed-off-by: Yury Polyanskiy <polyanskiy@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>