ipv6: record frag_max_size in atomic fragments in input path

Commit dbd1759e ("ipv6: on reassembly, record frag_max_size")
filled the frag_max_size field in IP6CB in the input path.
The field should also be filled in case of atomic fragments.

Fixes: dbd1759e ('ipv6: on reassembly, record frag_max_size')
Signed-off-by: Francesco Ruggeri <fruggeri@arista.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/reassembly.c

@@ -343,7 +343,7 @@ static int ipv6_frag_rcv(struct sk_buff *skb)
 	hdr = ipv6_hdr(skb);
 	fhdr = (struct frag_hdr *)skb_transport_header(skb);
 
-	if (!(fhdr->frag_off & htons(0xFFF9))) {
+	if (!(fhdr->frag_off & htons(IP6_OFFSET | IP6_MF))) {
 		/* It is not a fragmented frame */
 		skb->transport_header += sizeof(struct frag_hdr);
 		__IP6_INC_STATS(net,
@@ -351,6 +351,8 @@ static int ipv6_frag_rcv(struct sk_buff *skb)
 
 		IP6CB(skb)->nhoff = (u8 *)fhdr - skb_network_header(skb);
 		IP6CB(skb)->flags |= IP6SKB_FRAGMENTED;
+		IP6CB(skb)->frag_max_size = ntohs(hdr->payload_len) +
+					    sizeof(struct ipv6hdr);
 		return 1;
 	}