usb: rndis: reset ul aggregation stats for every set_alt

Resetting stats at every cable connection can help monitor
aggregation pattern from rndis host driver for every enumeration.
Enable these parameters to be accessed from debug files. Also
fix minor issue with module parameter description and counting
number packets during ul de-aggregation.

Change-Id: Ibfb0e2ee537e3dfbf583201bf79d5b8bcc5865a5
Signed-off-by: Vamsi Krishna <vskrishn@codeaurora.org>