peer: move atomic var increment in msgConsumer goroutine to defer

In this commit we move the atomic var increment that signals the
consumer goourtine has exited to the top of the method in a defer
statement. This cleans up some duplicate code and also adheres to the
pattern of using defers to signal cleaning up any dependent goroutine
state on exit.

peer.go

@@ -738,6 +738,7 @@ func (ms *msgStream) Stop() {
 func (ms *msgStream) msgConsumer() {
 	defer ms.wg.Done()
 	defer peerLog.Tracef(ms.stopMsg)
+	defer atomic.StoreInt32(&ms.streamShutdown, 1)
 
 	peerLog.Tracef(ms.startMsg)
 
@@ -754,7 +755,6 @@ func (ms *msgStream) msgConsumer() {
 			select {
 			case <-ms.quit:
 				ms.msgCond.L.Unlock()
-				atomic.StoreInt32(&ms.streamShutdown, 1)
 				return
 			default:
 			}
@@ -778,7 +778,6 @@ func (ms *msgStream) msgConsumer() {
 		select {
 		case ms.producerSema <- struct{}{}:
 		case <-ms.quit:
-			atomic.StoreInt32(&ms.streamShutdown, 1)
 			return
 		}
 	}