rpc, eth/filters: use non-blocking timer drain pattern

eth/filters/api.go

@@ -435,7 +435,10 @@ func (api *FilterAPI) GetFilterChanges(id rpc.ID) (interface{}, error) {
 		if !f.deadline.Stop() {
 			// timer expired but filter is not yet removed in timeout loop
 			// receive timer value and reset timer
-			<-f.deadline.C
+			select {
+			case <-f.deadline.C:
+			default:
+			}
 		}
 		f.deadline.Reset(api.timeout)
 

rpc/websocket.go

@@ -357,7 +357,10 @@ func (wc *websocketCodec) pingLoop() {
 
 		case <-wc.pingReset:
 			if !pingTimer.Stop() {
-				<-pingTimer.C
+				select {
+				case <-pingTimer.C:
+				default:
+				}
 			}
 			pingTimer.Reset(wsPingInterval)