netlink: fix some kernel-doc comments

Modify the comment of input parameter of nlmsg_ and nla_ function.

Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>
Link: https://lore.kernel.org/r/20220824013621.365103-1-shaozhengchao@huawei.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>