Revert "IPoIB: Use dedicated workqueues per interface"

This reverts commit 5141861cd5.

The series of IPoIB bug fixes that went into 3.19-rc1 introduce
regressions, and after trying to sort things out, we decided to revert
to 3.18's IPoIB driver and get things right for 3.20.

Signed-off-by: Roland Dreier <roland@purestorage.com>

drivers/infiniband/ulp/ipoib/ipoib.h

@@ -323,7 +323,6 @@ struct ipoib_dev_priv {
 	struct list_head multicast_list;
 	struct rb_root multicast_tree;
 
-	struct workqueue_struct *wq;
 	struct delayed_work mcast_task;
 	struct work_struct carrier_on_task;
 	struct work_struct flush_light;