IB/hfi1: Clean up user_sdma_send_pkts() function

user_sdma_send_pkts() function is unnecessarily long. Clean it up by
moving some of its code into separate functions.

Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Harish Chegondi <harish.chegondi@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>