can: raw: use temp variable instead of rolling back config

Introduce a temporary variable to check for an invalid configuration
attempt from user space. Before this patch the value was copied to
the real config variable and rolled back in the case of an error.

Suggested-by: Marc Kleine-Budde <[e-mail]>
Signed-off-by: Oliver Hartkopp <[e-mail]>
Link: https://lore.kernel.org/all/[e-mail]
Signed-off-by: Marc Kleine-Budde <[e-mail]>

net/can/raw.c

···
 	struct can_filter sfilter;         /* single filter */
 	struct net_device *dev = NULL;
 	can_err_mask_t err_mask = 0;
+	int fd_frames;
 	int count = 0;
 	int err = 0;
 
···
 		break;
 
 	case CAN_RAW_FD_FRAMES:
-		if (optlen != sizeof(ro->fd_frames))
+		if (optlen != sizeof(fd_frames))
 			return -EINVAL;
 
-		if (copy_from_sockptr(&ro->fd_frames, optval, optlen))
+		if (copy_from_sockptr(&fd_frames, optval, optlen))
 			return -EFAULT;
 
 		/* Enabling CAN XL includes CAN FD */
-		if (ro->xl_frames && !ro->fd_frames) {
-			ro->fd_frames = ro->xl_frames;
+		if (ro->xl_frames && !fd_frames)
 			return -EINVAL;
-		}
+
+		ro->fd_frames = fd_frames;
 		break;
 
 	case CAN_RAW_XL_FRAMES: