IB/SA: Split struct sa_path_rec based on IB and ROCE specific fields

sa_path_rec now contains a union of sa_path_rec_ib and sa_path_rec_roce
based on the type of the path record. Note that fields applicable to
path record type ROCE v1 and ROCE v2 fall under sa_path_rec_roce.
Accessor functions are added to these fields so the caller doesn't have
to know the type.

Reviewed-by: Don Hiatt <don.hiatt@intel.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Dasaratharaman Chandramouli <dasaratharaman.chandramouli@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>