Read /proc/net files with a single read syscall.

[wcc526]

https://github.com/prometheus/node_exporter/blob/master/collector/tcpstat_linux.go#L116

Please read /proc/net files with a single read syscall.

shirou/gopsutil#361

`for scanner.Scan() {
parts := strings.Fields(scanner.Text())
if len(parts) == 0 {
continue
}
if len(parts) < 4 {
return nil, fmt.Errorf("invalid TCP stats line: %q", scanner.Text())
}

	if strings.HasPrefix(parts[0], "sl") {
		continue
	}
	st, err := strconv.ParseInt(parts[3], 16, 8)
	if err != nil {
		return nil, err
	}

	tcpStats[tcpConnectionState(st)]++
}`

which maybe lead high memory usage

[discordianfish]

Very good point!