mmap_cache: "Override" functions for initgr mmap cache
Functions sss_mc_get_strs_offset and sss_mc_get_strs_len provides
data about strings for individual memory caches (passwd, ...)
Their are used in generic responder mmap cache code to find a record
in mmap cache (sss_mc_find_record). Data provided from functions sss_mc_get_*
are used for checking the validity of record. So in case of corrupted record
the whole mmap cache can be invalidated.
Functions sss_mc_get_strs_offset and sss_mc_get_strs_len did not provide
data for initgroups mmap cache and therefore particular record could not be
invalidated.
Resolves:
https://fedorahosted.org/sssd/ticket/2716
Reviewed-by: Michal Židek <mzidek@redhat.com>