diag: Identify apps data buffer with hdlc context

HDLC status of the buffer used in processing user space apps
packets is not known when freeing the buffer is leading to wrong
buffer freed and in turn possibly leading to resource starvation.
Using HDLC context to identify the buffer prevents the issue.

Change-Id: I7516f5ea56398372deaed3b41f33885bdbddc067
Signed-off-by: Manoj Prabhu B <bmanoj@codeaurora.org>