Pull request: all: opt log levels more

Updates #3929.

Squashed commit of the following:

commit 0d4aadeff1c4de1440795faf83eb072c46392ff3
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Tue Dec 28 16:34:44 2021 +0300

    all: opt log levels more

internal/dhcpd/v4.go

@@ -1056,8 +1056,6 @@ func (s *v4Server) Start() (err error) {
 	go func() {
 		if serr := s.srv.Serve(); errors.Is(serr, net.ErrClosed) {
 			log.Info("dhcpv4: server is closed")
-
-			return
 		} else if serr != nil {
 			log.Error("dhcpv4: srv.Serve: %s", serr)
 		}