net: rmnet_data: Optimize UL aggregation accumulation logic

Accumulation logic now respects max packet count as well as buffer size.
Additionally, packets will get shipped if they have been sitting around
for more than 1ms. This parameter is tunable from the module parameters
location.

CRs-Fixed: 772705
Change-Id: I1b5cb597ef6adfe19df590582f9a6cae091c5977
Signed-off-by: Harout Hedeshian <harouth@codeaurora.org>