p2p: Check peer threshold is met before giving up on ctx deadline (#12446)

Co-authored-by: prylabs-bulldozer[bot] <58059840+prylabs-bulldozer[bot]@users.noreply.github.com>

beacon-chain/p2p/subnets.go

@@ -62,13 +62,13 @@ func (s *Service) FindPeersWithSubnet(ctx context.Context, topic string,
 	currNum := len(s.pubsub.ListPeers(topic))
 	wg := new(sync.WaitGroup)
 	for {
+		if currNum >= threshold {
+			break
+		}
 		if err := ctx.Err(); err != nil {
 			return false, errors.Errorf("unable to find requisite number of peers for topic %s - "+
 				"only %d out of %d peers were able to be found", topic, currNum, threshold)
 		}
-		if currNum >= threshold {
-			break
-		}
 		nodes := enode.ReadNodes(iterator, int(params.BeaconNetworkConfig().MinimumPeersInSubnetSearch))
 		for _, node := range nodes {
 			info, _, err := convertToAddrInfo(node)