smbd: use vfs_stat() in more places

smbd: use vfs_stat() in more places

This replaces the code in a bunch of places where we choose between stat() and
lstat() based on req->posix_pathname. The new code inside vfs_stat() is based on
checking the smb_fname flag SMB_FILENAME_POSIX_PATH.

req->posix_pathname is inherited from the global POSIX pathnames state and the
smb_fname flags is also inherited from that indirectly via the UCF flags.

Tl;dr: no change in behaviour. :)

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>