Revert "pml/cm: fix buffer usage in MCA_PML_CM_HVY_SEND_REQUEST_BSEND_ALLOC()"

This reverts commit d71fe93.

The revert fixes a bug revealed by mtt ibm test suite. The send buffer,
instead of the attached user buffer, was used for MPI_Bsend.

This violates the MPI_Bsend semantic and makes it unsafe to reuse the
send buffer after the function returns.

The revert is also needed for 4.x

Signed-off-by: Wenduo Wang <wenduwan@amazon.com>

Author: wenduwan

ompi/mca/pml/cm/pml_cm_sendreq.h

@@ -381,7 +381,7 @@ do {                                                                    \
                                  &max_data );                           \
             opal_convertor_prepare_for_send( &sendreq->req_send.req_base.req_convertor, \
                                              &(ompi_mpi_packed.dt.super),  \
-                                             max_data, sendreq->req_addr ); \
+                                             max_data, sendreq->req_buff ); \
         }                                                               \
     }                                                                   \
  } while(0);