introduce new counter rlc_sent_dummy

rlc_sent_dummy count the amount of dummy package which are
sent in case no data packet is in the queue.

Change-Id: Ia60eab853d9145980f30d63e4ce4b520b8c51381
Reviewed-on: https://gerrit.osmocom.org/85
Tested-by: Jenkins Builder
Reviewed-by: Holger Freyther <holger@freyther.de>
3 files changed