Pull request: dnsfilter: imp code, decr cyclo

Updates #2646.

Squashed commit of the following:

commit c153f08bcf5ade4d0fb9b59d2a0e6a21598c4127
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Thu Mar 25 21:03:51 2021 +0300

    dnsfilter: imp code, decr cyclo

scripts/make/go-lint.sh

@@ -128,6 +128,12 @@ exit_on_output() (
 
 
 
+# Constants
+
+readonly go_files='./main.go ./tools.go ./internal/'
+
+
+
 # Checks
 
 exit_on_output blocklist_imports
@@ -142,11 +148,12 @@ golint --set_exit_status ./...
 
 "$GO" vet ./...
 
-gocyclo --over 19 .
+# Here and below, don't use quotes to get word splitting.
+gocyclo --over 18 $go_files
 
-gosec --quiet .
+gosec --quiet $go_files
 
-ineffassign .
+ineffassign ./...
 
 unparam ./...