igmp: Avoid zero delay when receiving odd mixture of IGMP queries

Commit 5b7c84066733c5dfb0e4016d939757b38de189e4 ('ipv4: correct IGMP
behavior on v3 query during v2-compatibility mode') added yet another
case for query parsing, which can result in max_delay = 0.  Substitute
a value of 1, as in the usual v3 case.

Reported-by: Simon McVittie <smcv@debian.org>
References: http://bugs.debian.org/654876
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>
static int igmpv3_sendpack(struct sk_buff *skb)
{
	struct igmphdr *pig = igmp_hdr(skb);
	const int igmplen = skb->tail - skb->transport_header;

	pig->csum = ip_compute_csum(igmp_hdr(skb), igmplen);

	return ip_local_out(skb);
}

static int igmpv3_sendpack(struct sk_buff *skb)
{
	struct igmphdr *pig = igmp_hdr(skb);
	const int igmplen = skb->tail - skb->transport_header;

	pig->csum = ip_compute_csum(igmp_hdr(skb), igmplen);

	return ip_local_out(skb);
}
