netfilter: Include alarm type timer in idletimer

This patch adds option for alarm type timer which can be used to
identify when interfaces have been idle for a certain period of time.

If timer_type is set for alarm from userspace, alarm type timer is
used. If more than one rule uses the same timer label, alarm will
be restarted whenever any of the rules get a hit. If rule with same
timer label is added for an alarm, it will continue with remaining
expiry time and will never reset.

With this change adding/replacing rule with same label and different
timer type is not allowed.

When the alarm expires, the target module sends a sysfs notification
to the userspace, which can then decide what to do.
Compared to current timer, alarm type timer can send notifications
when CPU is in suspend too, to notify the timer expiry.

Change-Id: Ibf3881c5e5979c535c946d208a9a0f0b6131dd11
Signed-off-by: Manoj Basapathi <manojbm@codeaurora.org>
Signed-off-by: Sauvik Saha <ssaha@codeaurora.org>