[9610] wlbt: traffic monitor - fix throughput report

[9610] wlbt: traffic monitor - fix throughput report

1) The traffic monitor uses a jiffies based timer
which is not exactly accurate as it is not a
High resolution timer.

The throughput calculation assumes the time to be
same as the timer interval. But it causes the
throughput report to be slightly off the mark.

Measure exact time diff between each timer
interrupt to report accurate throughput.

2) report throughput per second instead of per
timer interval.

3) Apply a rough correction to exclude IP and
transport header from payload size calculation.

Change-Id: Icf595b2bd694b2877b67484db0c0bb57ca8c64d5
SCSC-Bug-Id: SSB-40955
Signed-off-by: Debabrata Purohit <d.purohit@samsung.com>