IB/hfi1: Remove the use of add/remove RB function pointers

The usage of function pointers for RB node insertion
and removal in the expected receive code path was
meant to be a small performance optimization. However,
maintaining it, especially with the new MMU API, would
become more troublesome as the API is extended.

Since the performance optimization is minor, remove the
function pointers and replace with direct calls.

Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Reviewed-by: Dean Luick <dean.luick@intel.com>
Signed-off-by: Mitko Haralanov <mitko.haralanov@intel.com>
Signed-off-by: Jubin John <jubin.john@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>