IB: Change CQE "csum_ok" field to a bit flag

Use a bit in wc_flags rather then a whole integer to hold the
"checksum OK" flag.  By itself, this change doesn't reduce the size of
struct ib_wc on 64bit machines -- it stays on 56 bytes because of
padding.  However, it will allow to add more fields in the future
without enlarging the struct.  Also, it will let us have a unified
approach with future libibverbs checksum offload reporting, because a
bit flag doesn't break the library ABI.

This patch was suggested during conversation with Liran Liss
<liranl@mellanox.com>.

Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Reviewed-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

drivers/infiniband/hw/mlx4/cq.c

@@ -720,7 +720,8 @@ repoll:
 		wc->dlid_path_bits = (g_mlpath_rqpn >> 24) & 0x7f;
 		wc->wc_flags	  |= g_mlpath_rqpn & 0x80000000 ? IB_WC_GRH : 0;
 		wc->pkey_index     = be32_to_cpu(cqe->immed_rss_invalid) & 0x7f;
-		wc->csum_ok	   = mlx4_ib_ipoib_csum_ok(cqe->status, cqe->checksum);
+		wc->wc_flags	  |= mlx4_ib_ipoib_csum_ok(cqe->status,
+					cqe->checksum) ? IB_WC_IP_CSUM_OK : 0;
 		if (rdma_port_get_link_layer(wc->qp->device,
 				(*cur_qp)->port) == IB_LINK_LAYER_ETHERNET)
 			wc->sl  = be16_to_cpu(cqe->sl_vid) >> 13;