RDMA: Update workqueue usage

* ib_wq is added, which is used as the common workqueue for infiniband
  instead of the system workqueue.  All system workqueue usages
  including flush_scheduled_work() callers are converted to use and
  flush ib_wq.

* cancel_delayed_work() + flush_scheduled_work() converted to
  cancel_delayed_work_sync().

* qib_wq is removed and ib_wq is used instead.

This is to prepare for deprecation of flush_scheduled_work().

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Roland Dreier <rolandd@cisco.com>
diff --git a/include/rdma/ib_verbs.h b/include/rdma/ib_verbs.h
index e04c488..55cd0a0 100644
--- a/include/rdma/ib_verbs.h
+++ b/include/rdma/ib_verbs.h
@@ -47,10 +47,13 @@
 #include <linux/list.h>
 #include <linux/rwsem.h>
 #include <linux/scatterlist.h>
+#include <linux/workqueue.h>
 
 #include <asm/atomic.h>
 #include <asm/uaccess.h>
 
+extern struct workqueue_struct *ib_wq;
+
 union ib_gid {
 	u8	raw[16];
 	struct {