f2fs: fix to set inode->i_mode correctly for posix_acl_update_mode

We should update the ~S_IRWXUGO part of inode->i_mode in __setattr_copy,
because posix_acl_update_mode updates mode based on inode->i_mode,
which finally overwrites the ~S_IRWXUGO part of i_acl_mode with old i_mode.

Testcase to reproduce this bug:
0. adduser abc
1. mkfs.f2fs /dev/sdd
2. mount -t f2fs /dev/sdd /mnt/f2fs
3. mkdir /mnt/f2fs/test
4. setfacl -m u:abc:r /mnt/f2fs/test
5. chmod +s /mnt/f2fs/test
Signed-off-by: Weichao Guo <guoweichao@oppo.com>
Signed-off-by: Bin Shu <shubin@oppo.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/file.c

@@ -850,6 +850,7 @@ static void __setattr_copy(struct inode *inode, const struct iattr *attr)
 
 		if (!in_group_p(inode->i_gid) && !capable(CAP_FSETID))
 			mode &= ~S_ISGID;
+		inode->i_mode = (inode->i_mode & S_IRWXUGO) | (mode & ~S_IRWXUGO);
 		set_acl_inode(inode, mode);
 	}
 }