cherry-pick: 3157 excessive ptrs

Merge in DNS/adguard-home from 3157-excessive-ptrs to master

Updates #3157.

Squashed commit of the following:

commit 6803988240dca2f147bb80a5b3f78d7749d2fa14
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Tue Apr 19 14:50:01 2022 +0300

    aghnet: and again

commit 1a7f4d1dbc8fd4d3ae620349917526a75fa71b47
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Tue Apr 19 14:49:20 2022 +0300

    aghnet: docs again

commit d88da1fc7135f3cd03aff10b02d9957c8ffdfd30
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Tue Apr 19 14:47:36 2022 +0300

    aghnet: imp docs

commit c45dbc7800e882c6c4110aab640c32b03046f89a
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Tue Apr 19 14:41:19 2022 +0300

    aghnet: keep alphabetical order

commit b61781785d096ef43f60fb4f1905a4ed3cdf7c68
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Tue Apr 19 13:50:56 2022 +0300

    aghnet: imp code quality

commit 578dbd71ed2f2089c69343d7d4bf8bbc29150ace
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Tue Apr 12 17:02:38 2022 +0300

    aghnet: imp arp container

internal/aghos/os_windows.go

@@ -4,6 +4,10 @@
 package aghos
 
 import (
+	"os"
+	"os/signal"
+	"syscall"
+
 	"golang.org/x/sys/windows"
 )
 
@@ -35,3 +39,20 @@ func haveAdminRights() (bool, error) {
 func isOpenWrt() (ok bool) {
 	return false
 }
+
+func notifyShutdownSignal(c chan<- os.Signal) {
+	// syscall.SIGTERM is processed automatically.  See go doc os/signal,
+	// section Windows.
+	signal.Notify(c, os.Interrupt)
+}
+
+func isShutdownSignal(sig os.Signal) (ok bool) {
+	switch sig {
+	case
+		os.Interrupt,
+		syscall.SIGTERM:
+		return true
+	default:
+		return false
+	}
+}