xprtrdma: Reduce number of MRs created by rpcrdma_mrs_create

Create fewer MRs on average. Many workloads don't need as many as
32 MRs, and the transport can now quickly restock the MR free list.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

net/sunrpc/xprtrdma/verbs.c

@@ -1023,7 +1023,7 @@ rpcrdma_mrs_create(struct rpcrdma_xprt *r_xprt)
 	LIST_HEAD(free);
 	LIST_HEAD(all);
 
-	for (count = 0; count < 32; count++) {
+	for (count = 0; count < 3; count++) {
 		struct rpcrdma_mr *mr;
 		int rc;