openvswitch: Fix parsing invalid LLC/SNAP ethertypes

Before this patch, if an LLC/SNAP packet with OUI 00:00:00 had an
ethertype less than 1536 the flow key given to userspace in the upcall
would contain the invalid ethertype (for example, 3). If userspace
attempted to insert a kernel flow for this key it would be rejected
by ovs_flow_from_nlattrs.

This patch allows OVS to pass the OFTest pktact.DirectBadLlcPackets.

Signed-off-by: Rich Lane <rlane@bigswitch.com>
Signed-off-by: Jesse Gross <jesse@nicira.com>

net/openvswitch/flow.c

@@ -484,7 +484,11 @@ static __be16 parse_ethertype(struct sk_buff *skb)
 		return htons(ETH_P_802_2);
 
 	__skb_pull(skb, sizeof(struct llc_snap_hdr));
-	return llc->ethertype;
+
+	if (ntohs(llc->ethertype) >= 1536)
+		return llc->ethertype;
+
+	return htons(ETH_P_802_2);
 }
 
 static int parse_icmpv6(struct sk_buff *skb, struct sw_flow_key *key,