msm: net: ecm: outstanding packet counter peeking

The new debugfs entry allows the user to peek
at the current outstanding packets that were sent to
the IPA driver but not yet got Tx-complete notified.

Change-Id: I9b8d2b43bfb4a05da9c0ef8b6a6eda5d6961a8ca
Signed-off-by: Talel Atias <tatias@codeaurora.org>