net: usbnet: Add module param to toggle LTE IPC logs

IPC logging for LTE functions (RmNet/ECM) is hogging the CPU and
degrading the throughput. Add module parameter 'debug_mask' to
control these logs. By default, the value of ‘debug_mask’ is 0
which means no packets will be logged.

To enable all logs:
 echo 2 > /sys/module/usbnet/parameters/debug_mask

To enable only cv2x log:
 echo 1 > /sys/module/usbnet/parameters/debug_mask

To disable all logs (default setting on boot):
 echo 0 > /sys/module/usbnet/parameters/debug_mask

Change-Id: Id9497c95cbc8c76d0167cd858f7a36b6af12644d
Signed-off-by: Ajay Agarwal <ajaya@codeaurora.org>