Prefix VFS API macros with SMB_ for consistency and to avoid problems with VFS_ macro...

Prefix VFS API macros with SMB_ for consistency and to avoid problems with VFS_ macros at system side. We currently have one clash with AIX and its VFS_LOCK. Compiled and tested -- no new functionality or code, just plain rename of macros for yet-unreleased VFS API version. Needs to be done before a24 is out
(This used to be commit c2689ed118b490e49497a76ed6a2251262018769)