libsmb: Implement SMB_FIND_FILE_UNIX_INFO2 dir listing

libsmb: Implement SMB_FIND_FILE_UNIX_INFO2 dir listing

This keeps the original SMB_STRUCT_STAT coming from posix as part of
struct file_info. It is a slight waste of space, as the timestamps are
kept twice, but having a full SMB_STRUCT_STAT with the nlink!=0
validity check makes thinking about which mode/size/etc is the correct
one a no-brainer. We can save space later by referencing only one set
of time stamps for example.

This for the time fixes readdirplus2, but for the wrong reason: We don't yet
create files the "proper" way using posix create.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>