libbpf: Fix overrun in netlink attribute iteration

I accidentally found that a change in commit 1045b03e07d8 ("netlink: fix
overrun in attribute iteration") was not synchronized to the function
`nla_ok` in tools/lib/bpf/nlattr.c, I think it is necessary to modify,
this patch will do it.

Signed-off-by: Xin Liu <liuxin350@huawei.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220930090708.62394-1-liuxin350@huawei.com

tools/lib/bpf/nlattr.c

@@ -32,7 +32,7 @@ static struct nlattr *nla_next(const struct nlattr *nla, int *remaining)
 
 static int nla_ok(const struct nlattr *nla, int remaining)
 {
-	return remaining >= sizeof(*nla) &&
+	return remaining >= (int)sizeof(*nla) &&
 	       nla->nla_len >= sizeof(*nla) &&
 	       nla->nla_len <= remaining;
 }