svcrdma: Double the default credit limit

The RDMA credit limit controls how many concurrent RPCs are allowed
per connection.

An NFS/RDMA client and server exchange their credit limits in the
RPC/RDMA headers. The Linux client and the Solaris client and server
allow 32 credits. The Linux server allows only 16, which limits its
performance.

Set the server's default credit limit to 32, like the other well-
known implementations, so the out-of-the-shrinkwrap performance of
the Linux server is better.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

include/linux/sunrpc/svc_rdma.h

@@ -174,8 +174,7 @@ struct svcxprt_rdma {
  * page size of 4k, or 32k * 2 ops / 4k = 16 outstanding RDMA_READ.  */
 #define RPCRDMA_ORD             (64/4)
 #define RPCRDMA_SQ_DEPTH_MULT   8
-#define RPCRDMA_MAX_THREADS     16
-#define RPCRDMA_MAX_REQUESTS    16
+#define RPCRDMA_MAX_REQUESTS    32
 #define RPCRDMA_MAX_REQ_SIZE    4096
 
 /* svc_rdma_marshal.c */