staging/rdma/hfi1: Remove header memcpy from sdma send path.

staging/rdma/hfi1: Remove header memcpy from sdma send path.

Instead of writing the header into a buffer then copying it into another
buffer to be sent, remove that memcpy and instead build the header directly
into the tx request that will be sent.

Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Vennila Megavannan <vennila.megavannan@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>