also fix sysdb_svc_add declarations

Also allows us to remove sysdb_subdom_get<pw/gr>nam() wrappers and restore
fqnames proper value in subdomains, by testing for a parent domain being
present or not.

If use_fully_qualified_names is used, we need to pass fqdn
to sss_mmap_cache_*_invalidate.

If a fatal EFAULT error is returned by the internal function that frees used
memory invalidate the whole cache and reinit it. This way we avoid further
corruption and insure clients see consistent data.

Also insure we use the right context in init() and we use talloc_zfree() in
reinit so that if the init() later fails we do not leave around a pointer
to free memory in the callers.

We should never try to invalidate an already invalid record as
internal pointers will not be consistent. Carefully test that the
record really is valid when we are fishing for free space, and
properly invalidate records or return a fatal error if something
goes wrong.
In order to make the code more robust always invalidate the whole
data space on initialization by setting all bits to 1, and make sure
to invalidate the whole last allocated slot by converting rec->len to
the number of slots instead of just the space used.