Pull request: * all: move internal Go packages to internal/

Merge in DNS/adguard-home from 2234-move-to-internal to master

Squashed commit of the following:

commit d26a288cabeac86f9483fab307677b1027c78524
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Fri Oct 30 12:44:18 2020 +0300

    * all: move internal Go packages to internal/

    Closes #2234.

internal/util/network_utils_test.go

@@ -0,0 +1,24 @@
+package util
+
+import (
+	"log"
+	"testing"
+)
+
+func TestGetValidNetInterfacesForWeb(t *testing.T) {
+	ifaces, err := GetValidNetInterfacesForWeb()
+	if err != nil {
+		t.Fatalf("Cannot get net interfaces: %s", err)
+	}
+	if len(ifaces) == 0 {
+		t.Fatalf("No net interfaces found")
+	}
+
+	for _, iface := range ifaces {
+		if len(iface.Addresses) == 0 {
+			t.Fatalf("No addresses found for %s", iface.Name)
+		}
+
+		log.Printf("%v", iface)
+	}
+}