IB/hfi1: Create a routine to set a receive side mapping rule

Move the rule setting code into its own routine for improved
searchability and reuse.

Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Dean Luick <dean.luick@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>