plugin/forward: Fix incorrect failover counter reset (#8277)

* plugin/forward: Fix incorrect failover counter reset

This PR fixes the isseue where resetting the failover counter caused
retry the same upstreams until timeout instead of stopping after one pass.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* golint fix

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

---------

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

plugin/forward/forward.go

@@ -10,6 +10,7 @@ import (
 	"errors"
 	"net"
 	"net/http"
+	"slices"
 	"sync/atomic"
 	"time"
 
@@ -126,6 +127,7 @@ func (f *Forward) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg
 	}
 
 	fails := 0
+	failoverAttempts := 0
 	var span, child ot.Span
 	var upstreamErr error
 	span = ot.SpanFromContext(ctx)
@@ -236,16 +238,11 @@ func (f *Forward) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg
 
 		// Check if we have a failover Rcode defined, check if we match on the code
 		tryNext := false
-		for _, failoverRcode := range f.failoverRcodes {
-			// if we match, we continue to the next upstream in the list
-			if failoverRcode == ret.Rcode {
-				if fails < len(f.proxies) {
-					tryNext = true
-				}
-			}
+		if slices.Contains(f.failoverRcodes, ret.Rcode) {
+			failoverAttempts++
+			tryNext = failoverAttempts < len(f.proxies)
 		}
 		if tryNext {
-			fails++
 			continue
 		}