s3:lib: round itime to NTTIME resolution in make_file_id_from_itime()

s3:lib: round itime to NTTIME resolution in make_file_id_from_itime()

The rounding is needed because when a file is created via eg an SMB2 CREATE
request, we need to calculate the correct File-ID for the QFID Create-Context or
for a subsequent GETINFO SMB request on the same file-handle.

Any later metadata request that received the File-ID will do so by going through
dos_mode() -> ... -> parse_dos_attribute_blob(), where the File-ID will be
calculated from the on-disk itime which has NTTIME resolution.

As long as that is the only available itime backend, I'm rounding itime inside
make_file_id_from_itime(), not in the callers.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14121

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>