NFS: load the rpc/rdma transport module automatically

When mounting an NFS/RDMA server with the "-o proto=rdma" or
"-o rdma" options, attempt to dynamically load the necessary
"xprtrdma" client transport module. Doing so improves usability,
while avoiding a static module dependency and any unnecesary
resources.
Signed-off-by: NTom Talpey <tmtalpey@gmail.com>
Cc: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/super.c

@@ -1018,6 +1018,7 @@ static int nfs_parse_mount_options(char *raw,
 		case Opt_rdma:
 			mnt->flags |= NFS_MOUNT_TCP; /* for side protocols */
 			mnt->nfs_server.protocol = XPRT_TRANSPORT_RDMA;
+			xprt_load_transport(p);
 			break;
 		case Opt_acl:
 			mnt->flags &= ~NFS_MOUNT_NOACL;
@@ -1205,12 +1206,14 @@ static int nfs_parse_mount_options(char *raw,
 				/* vector side protocols to TCP */
 				mnt->flags |= NFS_MOUNT_TCP;
 				mnt->nfs_server.protocol = XPRT_TRANSPORT_RDMA;
+				xprt_load_transport(string);
 				break;
 			default:
 				errors++;
 				dfprintk(MOUNT, "NFS:   unrecognized "
 						"transport protocol\n");
 			}
+			kfree(string);
 			break;
 		case Opt_mountproto:
 			string = match_strdup(args);
@@ -1218,7 +1221,6 @@ static int nfs_parse_mount_options(char *raw,
 				goto out_nomem;
 			token = match_token(string,
 					    nfs_xprt_protocol_tokens, args);
-			kfree(string);
 
 			switch (token) {
 			case Opt_xprt_udp: