diag: Drop packets to avoid memory exhaustion

Added support to drop packets if more than 10
packets have accumulated in the rx list since usb
is not sending write done for previous packets sent
to usb to avoid memory exhaustion.

Change-Id: I44fe814abc5b199e1d1b86dcc6d0e2f043d15c49
Signed-off-by: Vivek Golani <vgolani@codeaurora.org>