We currently have inode_has_perm and dentry_has_perm.  dentry_has_perm just
calls inode_has_perm with additional audit data.  But dentry_has_perm can
take either a dentry or a path.  Split those to make the code obvious and
to fix the previous problem where I thought dentry_has_perm always had a
valid dentry and mnt.
Signed-off-by: NEric Paris <eparis@redhat.com>