ext4: allow defrag (EXT4_IOC_MOVE_EXT) in 32bit compat mode

I have an x86_64 kernel with i386 userspace. e4defrag fails on the
EXT4_IOC_MOVE_EXT ioctl because it is not wired up for the compat
case. It seems that struct move_extent is compat save, only types
with fixed widths are used:
{
        __u32 reserved;         /* should be zero */
        __u32 donor_fd;         /* donor file descriptor */
        __u64 orig_start;       /* logical start offset in block for orig */
        __u64 donor_start;      /* logical start offset in block for donor */
        __u64 len;              /* block length to be moved */
        __u64 moved_len;        /* moved block length */
};

Lets just wire up EXT4_IOC_MOVE_EXT for the compat case.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
CC: Akira Fujita <a-fujita@rs.jp.nec.com>

fs/ext4/ioctl.c

@@ -375,6 +375,8 @@ long ext4_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 		break;
 	case EXT4_IOC_GROUP_ADD:
 		break;
+	case EXT4_IOC_MOVE_EXT:
+		break;
 	default:
 		return -ENOIOCTLCMD;
 	}