nfs: kernel should return EPROTONOSUPPORT when not support NFSv4

  When nfs client(kernel) don't support NFSv4, maybe user build
  kernel without NFSv4, there is a problem.

  Using command "mount SERVER-IP:/nfsv3 /mnt/" to mount NFSv3
  filesystem, mount should should success, but fail and get error:

    "mount.nfs: an incorrect mount option was specified"

  System call mount "nfs"(not "nfs4") with "vers=4",
  if CONFIG_NFS_V4 is not defined, the "vers=4" will be parsed
  as invalid argument and kernel return EINVAL to nfs-utils.

  About that, we really want get EPROTONOSUPPORT rather than
  EINVAL. This path make sure kernel parses argument success,
  and return EPROTONOSUPPORT at nfs_validate_mount_data().
Signed-off-by: Mi Jinlong <mijinlong@cn.fujitsu.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/super.c

@@ -1069,12 +1069,10 @@ static int nfs_parse_mount_options(char *raw,
 			mnt->flags |= NFS_MOUNT_VER3;
 			mnt->version = 3;
 			break;
-#ifdef CONFIG_NFS_V4
 		case Opt_v4:
 			mnt->flags &= ~NFS_MOUNT_VER3;
 			mnt->version = 4;
 			break;
-#endif
 		case Opt_udp:
 			mnt->flags &= ~NFS_MOUNT_TCP;
 			mnt->nfs_server.protocol = XPRT_TRANSPORT_UDP;
@@ -1286,12 +1284,10 @@ static int nfs_parse_mount_options(char *raw,
 				mnt->flags |= NFS_MOUNT_VER3;
 				mnt->version = 3;
 				break;
-#ifdef CONFIG_NFS_V4
 			case NFS4_VERSION:
 				mnt->flags &= ~NFS_MOUNT_VER3;
 				mnt->version = 4;
 				break;
-#endif
 			default:
 				goto out_invalid_value;
 			}