net: qrtr: Add non blocking option for tx_resume

QRTR should support asynchronous sends even with the tx flow control
enabled. Add a timeout to the tx_wait and send a zero size packet to
nonblocking sockets after the remote port is no longer flow controlled.
This zero size packet will act as a notification for clients to start
sending again.

This change squashes the following commits from msm-4.14:
  commit 5dff60d7bb53 ("net: qrtr: Add non blocking option for tx_resume")
  commit aff4c897bcf5 ("net: qrtr: Fix missing resume_tx notification")
  commit c969cce741fc ("net: qrtr: Rearrange tx wait and protect critical
                        section")

In addition fix minor format issues.

Change-Id: I4b2a145b9507aa18ff08ef58e5620b72952f7f5f
Signed-off-by: Chris Lew <clew@codeaurora.org>