prometheus/blackbox_exporter: prober/utils.go; 25 LoC

Found a possible issue in [prometheus/blackbox_exporter](https://www.github.com/prometheus/blackbox_exporter) at [prober/utils.go](https://github.com/prometheus/blackbox_exporter/blob/998037b5b40c1de5fee348ffdea8820509d85171/prober/utils.go#L75-L99)

Below is the message reported by the analyzer for this snippet of code. Beware that the analyzer only reports the first issue it finds, so please do not limit your consideration to the contents of the below message.

> reference to ip is reassigned at line 86

[Click here to see the code in its original context.](https://github.com/prometheus/blackbox_exporter/blob/998037b5b40c1de5fee348ffdea8820509d85171/prober/utils.go#L75-L99)

Click here to show the 25 line(s) of Go which triggered the analyzer.

```go
for _, ip := range ips {
switch IPProtocol {
case "ip4":
if ip.IP.To4() != nil {
level.Info(logger).Log("msg", "Resolved target address", "ip", ip.String())
probeIPProtocolGauge.Set(4)
probeIPAddrHash.Set(ipHash(ip.IP))
return &ip, lookupTime, nil
}

// ip4 as fallback
fallback = &ip

case "ip6":
if ip.IP.To4() == nil {
level.Info(logger).Log("msg", "Resolved target address", "ip", ip.String())
probeIPProtocolGauge.Set(6)
probeIPAddrHash.Set(ipHash(ip.IP))
return &ip, lookupTime, nil
}

// ip6 as fallback
fallback = &ip
}
}

```

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commit ID: 998037b5b40c1de5fee348ffdea8820509d85171