fix: netstat inOut interval

[chaos-zhu]

• methods: netstat.inOut(interval):Promise(Object) [interval]: number - interval millisecond. defaulta: 1000

I think inputMb and outputMb should not be affected by interval. Please correct any mistakes

// Compute input output
metrics[oldStats[i].interface]['inputMb'] = parseFloat(((newStats[i].inputBytes - oldStats[i].inputBytes) / interval * 1000 / 1000000).toFixed(2))
metrics[oldStats[i].interface]['outputMb'] = parseFloat(((newStats[i].outputBytes - oldStats[i].outputBytes) / interval * 1000 / 1000000).toFixed(2))

// When I get it every 10 seconds, it's no longer accurate
netstat.inOut(10*1000) // 10s