fix: fix slice init length (vdaas#2672)

Co-authored-by: Yusuke Kato <kpango@vdaas.org>

internal/net/grpc/client.go

@@ -155,7 +155,7 @@ func (g *gRPCClient) StartConnectionMonitor(ctx context.Context) (<-chan error,
 	}
 	g.monitorRunning.Store(true)
 
-	addrs := make([]string, len(g.addrs))
+	addrs := make([]string, 0, len(g.addrs))
 	for addr := range g.addrs {
 		addrs = append(addrs, addr)
 	}