RDMA/rxe: Remove type 2A memory window capability

Currently the rdma_rxe driver claims to support both 2A and 2B type memory
windows. But the IBA requires

	010-37.2.31: If an HCA supports the Base Memory Management
	extensions, the HCA shall support either Type 2A or Type 2B MWs,
	but not both.

This commit removes the device capability bit for type 2A memory windows
and adds a clarifying comment to rxe_mw.c.

Link: https://lore.kernel.org/r/20220407184321.14207-1-rpearsonhpe@gmail.com
Signed-off-by: Bob Pearson <rpearsonhpe@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/infiniband/sw/rxe/rxe_mw.c

@@ -3,6 +3,14 @@
  * Copyright (c) 2020 Hewlett Packard Enterprise, Inc. All rights reserved.
  */
 
+/*
+ * The rdma_rxe driver supports type 1 or type 2B memory windows.
+ * Type 1 MWs are created by ibv_alloc_mw() verbs calls and bound by
+ * ibv_bind_mw() calls. Type 2 MWs are also created by ibv_alloc_mw()
+ * but bound by bind_mw work requests. The ibv_bind_mw() call is converted
+ * by libibverbs to a bind_mw work request.
+ */
+
 #include "rxe.h"
 
 int rxe_alloc_mw(struct ib_mw *ibmw, struct ib_udata *udata)

drivers/infiniband/sw/rxe/rxe_param.h

@@ -51,7 +51,6 @@ enum rxe_device_param {
 					| IB_DEVICE_SRQ_RESIZE
 					| IB_DEVICE_MEM_MGT_EXTENSIONS
 					| IB_DEVICE_MEM_WINDOW
-					| IB_DEVICE_MEM_WINDOW_TYPE_2A
 					| IB_DEVICE_MEM_WINDOW_TYPE_2B,
 	RXE_MAX_SGE			= 32,
 	RXE_MAX_WQE_SIZE		= sizeof(struct rxe_send_wqe) +