netfilter: remove comments that predate rcu days

We cannot block/sleep on nf_iterate because netfilter runs under rcu
read lock these days, where blocking is well-known to be illegal. So
let's remove these old comments.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/core.c

@@ -308,18 +308,11 @@ unsigned int nf_iterate(struct sk_buff *skb,
 {
 	unsigned int verdict;
 
-	/*
-	 * The caller must not block between calls to this
-	 * function because of risk of continuing from deleted element.
-	 */
 	while (*entryp) {
 		if (state->thresh > (*entryp)->ops.priority) {
 			*entryp = rcu_dereference((*entryp)->next);
 			continue;
 		}
-
-		/* Optimization: we don't need to hold module
-		   reference here, since function can't sleep. --RR */
 repeat:
 		verdict = (*entryp)->ops.hook((*entryp)->ops.priv, skb, state);
 		if (verdict != NF_ACCEPT) {