A race condition resulted in receive buffers being placed in the free list
twice.

Change the locking and handling to check whether the "other" path will be
freeing the entry in a later thread and skip it if it is.
Signed-off-by: Dick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: James Smart <jsmart2021@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>