Use strscpy instead of strlcpy if available

[MonterraByte]

Linux 6.8 removed strlcpy, so using strscpy is necessary on newer kernels.

(Another way of implementing this would be to #define strlcpy strscpy, but it's not very explicit.)

• Closes: https://github.com/umlaeute/v4l2loopback/issues/570
• Closes: https://github.com/umlaeute/v4l2loopback/issues/574