VFS: Modify opendir to take a const struct smb_filename * instead of const char *

VFS: Modify opendir to take a const struct smb_filename * instead of const char *

Preparing to reduce use of lp_posix_pathnames().

Uses the same techniques as commit 616d068f0cebb8e50a855b6e30f36fccb7f5a3c8
(synthetic_smb_fname()) to cope with modules that
modify the incoming pathname.

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