Fix a couple of code scanning alerts (#5157)

This PR fixed a couple of code scanning alerts:
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

plugin/forward/setup.go

@@ -163,13 +163,10 @@ func parseBlock(c *caddy.Controller, f *Forward) error {
 		if !c.NextArg() {
 			return c.ArgErr()
 		}
-		n, err := strconv.Atoi(c.Val())
+		n, err := strconv.ParseUint(c.Val(), 10, 32)
 		if err != nil {
 			return err
 		}
-		if n < 0 {
-			return fmt.Errorf("max_fails can't be negative: %d", n)
-		}
 		f.maxfails = uint32(n)
 	case "health_check":
 		if !c.NextArg() {

plugin/whoami/whoami.go

@@ -45,7 +45,7 @@ func (wh Whoami) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg)
 	if state.QName() == "." {
 		srv.Hdr.Name = "_" + state.Proto() + state.QName()
 	}
-	port, _ := strconv.Atoi(state.Port())
+	port, _ := strconv.ParseUint(state.Port(), 10, 16)
 	srv.Port = uint16(port)
 	srv.Target = "."