Currently, same user can be processed multiple times, which leads to
release ref count wrongly, with this, some of the users in PPDU
desc are never processed and can possibly cause memory leak.
Added a flag in PPDU user to indicate that the user is already
processed.
CRs-Fixed: 2718150
Change-Id: Ia00e0ad12999578157e9f8a6df0ad4763f828c88