SUNRPC: Use sysfs_emit in place of strlcpy/sprintf

Part of an effort to remove strlcpy() tree-wide [1].

Direct replacement is safe here since the getter in kernel_params_ops
handles -errno return [2].

[1] https://github.com/KSPP/linux/issues/89
[2] https://elixir.bootlin.com/linux/v6.4-rc6/source/include/linux/moduleparam.h#L52



Signed-off-by: Azeem Shaikh <azeemshaikh38@gmail.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>