usb: rndis: Add ul aggregation stats info to debug files

Enable UL aggregation stats to be accessed from debug
files. Also fix minor issue with counting number of
packets during ul de-aggregation.

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