ipv4: prevent potential spectre v1 gadget in fib_metrics_match()

In the Linux kernel, the following vulnerability has been resolved: ipv4: prevent potential spectre v1 gadget in fib_metrics_match() if (!type) continue; if (type > RTAX_MAX) return false; ... fi_val = fi->fib_metrics->metrics[type - 1]; @type being used as an array index, we need to prevent cpu speculation or risk leaking kernel memory content.