netfilter: xtables: Add snapshot of hardidletimer target

This is a snapshot of hardifletimer netfilter target as of msm-4.4
commit 469a150b7426 ("netfilter: xtables: hardidletimer target implementation")

This patch implements a hardidletimer Xtables target that can be
used to identify when interfaces have been idle for a certain period
of time.

Timers are identified by labels and are created when a rule is set
with a new label. The rules also take a timeout value (in seconds) as
an option. If more than one rule uses the same timer label, the timer
will be restarted whenever any of the rules get a hit.

One entry for each timer is created in sysfs. This attribute contains
the timer remaining for the timer to expire. The attributes are
located under the xt_idletimer class:

/sys/class/xt_hardidletimer/timers/<label>

When the timer expires, the target module sends a sysfs notification
to the userspace, which can then decide what to do (eg. disconnect to
save power)

Compared to xt_IDLETIMER, xt_HARDIDLETIMER can send notifications when
CPU is in suspend too, to notify the timer expiry.

CRs-Fixed: 1078373
Change-Id: Ib2e05af7267f3c86d1967f149f7e7e782c59807e
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>