fix wrong algorithm in WifiPowerPerPacket()

step1: PowerProfile.POWER_WIFI_ACTIVE represents energy consumption(mAh) per hour
devied by 3600, then WIFI_POWER ==> energy consumption(mAh) per second

step2: WIFI_BPS represents 1000000 bit per second
then (double)WIFI_BPS) / 8  ==> 1000000/8 Byte per second

step3: as upload and download, so divided  by 2;
then   (((double)WIFI_BPS) / 8 / 2048))  ==> 1000000/8/2048 KB per second
==> packet  per second (where 1 packet = 2 KB)

so WIFI_POWER / (((double)WIFI_BPS) / 8 / 2048) represents  mAh per Packet where 1 packet = 2 K.

when  divided by (60*60) again , that make WifiPowerEstimator narrow 3600 times.

Change-Id: Ic055a5145b6dfb1129c8969826329a3024c9e2b6
Signed-off-by: yuanhuihui <yuanhuihui@xiaomi.com>