fs: make posix_acl_chmod more useful

Rename the current posix_acl_chmod to __posix_acl_chmod and add
a fully featured ACL chmod helper that uses the ->set_acl inode
operation.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/9p/acl.c b/fs/9p/acl.c
index 7af425f..f5ce5c5 100644
--- a/fs/9p/acl.c
+++ b/fs/9p/acl.c
@@ -156,7 +156,7 @@
 		return -EOPNOTSUPP;
 	acl = v9fs_get_cached_acl(inode, ACL_TYPE_ACCESS);
 	if (acl) {
-		retval = posix_acl_chmod(&acl, GFP_KERNEL, inode->i_mode);
+		retval = __posix_acl_chmod(&acl, GFP_KERNEL, inode->i_mode);
 		if (retval)
 			return retval;
 		set_cached_acl(inode, ACL_TYPE_ACCESS, acl);