Pull request: all: fix lint and naming issues vol. 2

Merge in DNS/adguard-home from 2276-fix-lint-2 to master

Updates #2276.

Squashed commit of the following:

commit 24760b9586bb31be134ef9518dbece485560b1a0
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Mon Dec 7 14:39:50 2020 +0300

    all: fix lint and naming issues vol. 2

internal/dhcpd/checkother_windows.go

@@ -0,0 +1,11 @@
+package dhcpd
+
+import "fmt"
+
+func CheckIfOtherDHCPServersPresentV4(ifaceName string) (bool, error) {
+	return false, fmt.Errorf("not supported")
+}
+
+func CheckIfOtherDHCPServersPresentV6(ifaceName string) (bool, error) {
+	return false, fmt.Errorf("not supported")
+}