net: fix nla_policy_len to actually _iterate_ over the policy

Currently nla_policy_len always returns n * NLA_HDRLEN:
It loops, but does not advance it's iterator.
NLA_UNSPEC == 0 does not contain a .len in any policy.

Trivially fixed by adding p++.
Signed-off-by: NLars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

lib/nlattr.c

@@ -148,7 +148,7 @@ nla_policy_len(const struct nla_policy *p, int n)
 {
 	int i, len = 0;
 
-	for (i = 0; i < n; i++) {
+	for (i = 0; i < n; i++, p++) {
 		if (p->len)
 			len += nla_total_size(p->len);
 		else if (nla_attr_minlen[p->type])