net: rmnet_data: Switch aggregation from delayed work to hrtimer

The delay argument in schedule_delayed_work(struct delayed_work
*dwork, unsigned long delay) API is jiffies. The system tick for
seems to be 100Hz, so the minimum time resolution for the work to
be scheduled is 10ms.

Switch to hrtimer to achieve 1 ms granularity with a current timer
of 3ms for the flush thread.

CRs-fixed: 2147503
Change-Id: If33fea37146f91b2980e6637db71567fb5ca12a5
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>