xprtrdma: mount reports "Invalid mount option" if memreg mode not supported

If the selected memory registration mode is not supported by the
underlying provider/HCA, the NFS mount command reports that there was
an invalid mount option, and fails. This is misleading.

Reporting a problem allocating memory is a lot closer to the truth.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

net/sunrpc/xprtrdma/verbs.c

@@ -513,7 +513,7 @@ rpcrdma_ia_open(struct rpcrdma_xprt *xprt, struct sockaddr *addr, int memreg)
 #if RPCRDMA_PERSISTENT_REGISTRATION
 			memreg = RPCRDMA_ALLPHYSICAL;
 #else
-			rc = -EINVAL;
+			rc = -ENOMEM;
 			goto out2;
 #endif
 		}
@@ -554,9 +554,9 @@ rpcrdma_ia_open(struct rpcrdma_xprt *xprt, struct sockaddr *addr, int memreg)
 		}
 		break;
 	default:
-		printk(KERN_ERR "%s: invalid memory registration mode %d\n",
-				__func__, memreg);
-		rc = -EINVAL;
+		printk(KERN_ERR "RPC: Unsupported memory "
+				"registration mode: %d\n", memreg);
+		rc = -ENOMEM;
 		goto out2;
 	}
 	dprintk("RPC:       %s: memory registration strategy is %d\n",