IPoIB: Stop lying about hard_header_len and use skb->cb to stash LL addresses

Commit a0417fa3a18a ("net: Make qdisc_skb_cb upper size bound
explicit.") made it possible for a netdev driver to use skb->cb
between its header_ops.create method and its .ndo_start_xmit
method.  Use this in ipoib_hard_header() to stash away the LL address
(GID + QPN), instead of the "ipoib_pseudoheader" hack.  This allows
IPoIB to stop lying about its hard_header_len, which will let us fix
the L2 check for GRO.

Signed-off-by: Roland Dreier <roland@purestorage.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/infiniband/ulp/ipoib/ipoib.h b/drivers/infiniband/ulp/ipoib/ipoib.h
index b3cc1e0..86df632 100644
--- a/drivers/infiniband/ulp/ipoib/ipoib.h
+++ b/drivers/infiniband/ulp/ipoib/ipoib.h
@@ -44,6 +44,7 @@
 #include <linux/mutex.h>
 
 #include <net/neighbour.h>
+#include <net/sch_generic.h>
 
 #include <linux/atomic.h>
 
@@ -117,8 +118,9 @@
 	u16	reserved;
 };
 
-struct ipoib_pseudoheader {
-	u8  hwaddr[INFINIBAND_ALEN];
+struct ipoib_cb {
+	struct qdisc_skb_cb	qdisc_cb;
+	u8			hwaddr[INFINIBAND_ALEN];
 };
 
 /* Used for all multicast joins (broadcast, IPv4 mcast and IPv6 mcast) */