abci: minor cleanups in the socket client (#3758)

Follow up from #3512

Specifically:

    cli.conn.Close() need not be under the mutex (#3512 (comment))
    call the reqRes callback after the resCb so they always happen in the same order (#3512)

Fixes #3513

abci/client/socket_client.go

@@ -55,10 +55,6 @@ func NewSocketClient(addr string, mustConnect bool) *socketClient {
 }
 
 func (cli *socketClient) OnStart() error {
-	if err := cli.BaseService.OnStart(); err != nil {
-		return err
-	}
-
 	var err error
 	var conn net.Conn
 RETRY_LOOP:
@@ -82,15 +78,12 @@ RETRY_LOOP:
 }
 
 func (cli *socketClient) OnStop() {
-	cli.BaseService.OnStop()
-
-	cli.mtx.Lock()
-	defer cli.mtx.Unlock()
 	if cli.conn != nil {
-		// does this really need a mutex?
 		cli.conn.Close()
 	}
 
+	cli.mtx.Lock()
+	defer cli.mtx.Unlock()
 	cli.flushQueue()
 }
 
@@ -209,19 +202,18 @@ func (cli *socketClient) didRecvResponse(res *types.Response) error {
 	reqres.Done()            // Release waiters
 	cli.reqSent.Remove(next) // Pop first item from linked list
 
+	// Notify client listener if set (global callback).
+	if cli.resCb != nil {
+		cli.resCb(reqres.Request, res)
+	}
+
 	// Notify reqRes listener if set (request specific callback).
 	// NOTE: it is possible this callback isn't set on the reqres object.
 	// at this point, in which case it will be called after, when it is set.
-	// TODO: should we move this after the resCb call so the order is always consistent?
 	if cb := reqres.GetCallback(); cb != nil {
 		cb(res)
 	}
 
-	// Notify client listener if set (global callback).
-	if cli.resCb != nil {
-		cli.resCb(reqres.Request, res)
-	}
-
 	return nil
 }