fix: ignore missing /proc/net/tcp6 and /proc/net/udp6 on IPv6-disabled systems

Signed-off-by: Shouhei <shouhei.yamaguchi.be@gmail.com>

Author: shouhei

pkg/portutil/procnet/procnet_linux.go

@@ -18,6 +18,7 @@ package procnet
 
 import (
 	"bufio"
+	"errors"
 	"fmt"
 	"os"
 )
@@ -52,6 +53,10 @@ func ReadStatsFileData(protocol string) ([]string, error) {
 
 	fp, err := os.Open(fileAddress)
 	if err != nil {
+		// IPv6-disabled environments do not have these files.
+		if (fileAddress == netTCP6Stats || fileAddress == netUDP6Stats) && errors.Is(err, os.ErrNotExist) {
+			return nil, nil
+		}
 		return nil, err
 	}
 	defer fp.Close()