ksmbd: use vfs_remove_acl()

The current way of setting and getting posix acls through the generic
xattr interface is error prone and type unsafe. The vfs needs to
interpret and fixup posix acls before storing or reporting it to
userspace. Various hacks exist to make this work. The code is hard to
understand and difficult to maintain in it's current form. Instead of
making this work by hacking posix acls through xattr handlers we are
building a dedicated posix acl api around the get and set inode
operations. This removes a lot of hackiness and makes the codepaths
easier to maintain. A lot of background can be found in [1].

Now that we've switched all filesystems that can serve as the lower
filesystem for ksmbd we can switch ksmbd over to rely on
the posix acl api. Note that this is orthogonal to switching the vfs
itself over.

Link: https://lore.kernel.org/all/20220801145520.1532837-1-brauner@kernel.org [1]
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>

fs/ksmbd/vfs.c

@@ -1321,7 +1321,7 @@ int ksmbd_vfs_remove_acl_xattrs(struct user_namespace *user_ns,
 			     sizeof(XATTR_NAME_POSIX_ACL_ACCESS) - 1) ||
 		    !strncmp(name, XATTR_NAME_POSIX_ACL_DEFAULT,
 			     sizeof(XATTR_NAME_POSIX_ACL_DEFAULT) - 1)) {
-			err = ksmbd_vfs_remove_xattr(user_ns, dentry, name);
+			err = vfs_remove_acl(user_ns, dentry, name);
 			if (err)
 				ksmbd_debug(SMB,
 					    "remove acl xattr failed : %s\n", name);