IB: split struct ib_send_wr

This patch split up struct ib_send_wr so that all non-trivial verbs
use their own structure which embedds struct ib_send_wr.  This dramaticly
shrinks the size of a WR for most common operations:

sizeof(struct ib_send_wr) (old):	96

sizeof(struct ib_send_wr):		48
sizeof(struct ib_rdma_wr):		64
sizeof(struct ib_atomic_wr):		96
sizeof(struct ib_ud_wr):		88
sizeof(struct ib_fast_reg_wr):		88
sizeof(struct ib_bind_mw_wr):		96
sizeof(struct ib_sig_handover_wr):	80

And with Sagi's pending MR rework the fast registration WR will also be
down to a reasonable size:

sizeof(struct ib_fastreg_wr):		64

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bart.vanassche@sandisk.com> [srp, srpt]
Reviewed-by: Chuck Lever <chuck.lever@oracle.com> [sunrpc]
Tested-by: Haggai Eran <haggaie@mellanox.com>
Tested-by: Sagi Grimberg <sagig@mellanox.com>
Tested-by: Steve Wise <swise@opengridcomputing.com>
diff --git a/net/rds/iw.h b/net/rds/iw.h
index cbe6674..fe858e5 100644
--- a/net/rds/iw.h
+++ b/net/rds/iw.h
@@ -77,7 +77,11 @@
 	struct ib_fast_reg_page_list *s_page_list;
 	unsigned char		s_remap_count;
 
-	struct ib_send_wr	s_wr;
+	union {
+		struct ib_send_wr	s_send_wr;
+		struct ib_rdma_wr	s_rdma_wr;
+		struct ib_fast_reg_wr	s_fast_reg_wr;
+	};
 	struct ib_sge		s_sge[RDS_IW_MAX_SGE];
 	unsigned long		s_queued;
 };