CACHE_REQ: Add cache_req_data_get_type()
Adds a utility function which returns the lookup type stored in struct
cache_req_data. This will be used later to switch between different
lookups as appropriate.
Related:
https://pagure.io/SSSD/sssd/issue/3822
Reviewed-by: Michal Židek <mzidek@redhat.com>
(cherry picked from commit 2efc41cdd611d1e615dadae6324b096a23ae6659)