Fix a regression in the af_packet code that was breaking PPPoE

pppd sends packets with only a header and no payload.

Signed-off-by: Felix Fietkau <nbd@nbd.name>

--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2112,7 +2112,7 @@ static void tpacket_destruct_skb(struct
 static bool ll_header_truncated(const struct net_device *dev, int len)
 {
 	/* net device doesn't like empty head */
-	if (unlikely(len <= dev->hard_header_len)) {
+	if (unlikely(len < dev->hard_header_len)) {
 		net_warn_ratelimited("%s: packet size is too short (%d <= %d)\n",
 				     current->comm, len, dev->hard_header_len);
 		return true;