Fix slow nfq shutdown

Gopkg.lock

@@ -140,15 +140,15 @@
   revision = "2bc1f35cddc0cc527b4bc3dce8578fc2a6c11384"
 
 [[projects]]
-  branch = "master"
-  digest = "1:1f6a000c4fe2eaf76f506ecc23e859e1a5b81c0ec3039c5fca21bfbb80c43979"
+  digest = "1:711ec17a2d8edd94cff8e2e4339d847e46acc1bb6b49ec29dcc1db78b666378b"
   name = "github.com/mdlayher/netlink"
   packages = [
     ".",
     "nlenc",
   ]
   pruneopts = ""
-  revision = "ded538f7f4be5ec9a64b7a16c7fdb0bc66bfb85b"
+  revision = "2a4e26491f1ba4eae173a7733ac11744cfed82b5"
+  version = "v1.2.0"
 
 [[projects]]
   digest = "1:508f444b8e00a569a40899aaf5740348b44c305d36f36d4f002b277677deef95"

Gopkg.toml

@@ -32,4 +32,4 @@ ignored = ["github.com/safing/portbase/*", "github.com/safing/spn/*"]
 
 [[override]]
   name = "github.com/mdlayher/netlink"
-  branch = "master" # remove when https://github.com/mdlayher/netlink/pull/171 is released and in github.com/florianl/go-nfqueue
+  version = "1.2.0" # remove when github.com/florianl/go-nfqueue has updated to v1.2.0

firewall/interception/nfq/nfq.go

@@ -6,6 +6,7 @@ package nfq
 import (
 	"context"
 	"runtime"
+	"strings"
 	"sync/atomic"
 	"time"
 
@@ -140,7 +141,15 @@ func (q *Queue) handleError(e error) int {
 			return 0
 		}
 	}
-	log.Errorf("nfqueue: encountered error while receiving packets: %s\n", e.Error())
+
+	// Check if the queue was already closed. Unfortunately, the exposed error
+	// variable is in an internal stdlib package. Therefore, check for the error
+	// string instead. :(
+	// Offical error variable is defined here:
+	// https://github.com/golang/go/blob/0e85fd7561de869add933801c531bf25dee9561c/src/internal/poll/fd.go#L24
+	if !strings.HasSuffix(e.Error(), "use of closed file") {
+		log.Errorf("nfqueue: encountered error while receiving packets: %s\n", e.Error())
+	}
 
 	// Close the existing socket
 	if nf := q.getNfq(); nf != nil {