sunrpc/xprtrdma: clean up workqueue usage

* Create and use svc_rdma_wq instead of using the system workqueue and
  flush_scheduled_work().  This workqueue is necessary to serve as
  flushing domain for rdma->sc_work which is used to destroy itself
  and thus can't be flushed explicitly.

* Replace cancel_delayed_work() + flush_scheduled_work() with
  cancel_delayed_work_sync().

* Implement synchronous connect in xprt_rdma_connect() using
  flush_delayed_work() on the rdma_connect work instead of using
  flush_scheduled_work().

This is to prepare for the deprecation and removal of
flush_scheduled_work().

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
diff --git a/net/sunrpc/xprtrdma/transport.c b/net/sunrpc/xprtrdma/transport.c
index 2da32b4..0867070 100644
--- a/net/sunrpc/xprtrdma/transport.c
+++ b/net/sunrpc/xprtrdma/transport.c
@@ -237,8 +237,7 @@
 
 	dprintk("RPC:       %s: called\n", __func__);
 
-	cancel_delayed_work(&r_xprt->rdma_connect);
-	flush_scheduled_work();
+	cancel_delayed_work_sync(&r_xprt->rdma_connect);
 
 	xprt_clear_connected(xprt);
 
@@ -448,7 +447,7 @@
 	} else {
 		schedule_delayed_work(&r_xprt->rdma_connect, 0);
 		if (!RPC_IS_ASYNC(task))
-			flush_scheduled_work();
+			flush_delayed_work(&r_xprt->rdma_connect);
 	}
 }