Wait for GRO loop to stop

...before returning from groDispatcher.close.

This is to make sure that when we return from cleanup functions, the
caller can safely assume that resources have been released.

PiperOrigin-RevId: 493714729

pkg/tcpip/stack/gro.go

@@ -223,6 +223,7 @@ type groDispatcher struct {
 	stop chan struct{}
 
 	buckets [groNBuckets]groBucket
+	wg      sync.WaitGroup
 }
 
 func (gd *groDispatcher) init(interval time.Duration) {
@@ -246,7 +247,11 @@ func (gd *groDispatcher) init(interval time.Duration) {
 // start spawns a goroutine that flushes the GRO periodically based on the
 // interval.
 func (gd *groDispatcher) start(interval time.Duration) {
+	gd.wg.Add(1)
+
 	go func(interval time.Duration) {
+		defer gd.wg.Done()
+
 		var ch <-chan time.Time
 		if interval == 0 {
 			// Never run.
@@ -496,6 +501,7 @@ func (gd *groDispatcher) flushAll() {
 // close stops the GRO goroutine and releases any held packets.
 func (gd *groDispatcher) close() {
 	gd.stop <- struct{}{}
+	gd.wg.Wait()
 
 	for i := range gd.buckets {
 		bucket := &gd.buckets[i]