net: hsr: fix mac_len checks

Commit 2e9f60932a2c ("net: hsr: check skb can contain struct hsr_ethhdr
in fill_frame_info") added the following which resulted in -EINVAL
always being returned:
	if (skb->mac_len < sizeof(struct hsr_ethhdr))
		return -EINVAL;

mac_len was not being set correctly so this check completely broke
HSR/PRP since it was always 14, not 20.

Set mac_len correctly and modify the mac_len checks to test in the
correct places since sometimes it is legitimately 14.

Fixes: 2e9f60932a2c ("net: hsr: check skb can contain struct hsr_ethhdr in fill_frame_info")
Signed-off-by: George McCollister <george.mccollister@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/hsr/hsr_device.c b/net/hsr/hsr_device.c
index bfcdc75..26c3240 100644
--- a/net/hsr/hsr_device.c
+++ b/net/hsr/hsr_device.c
@@ -218,6 +218,7 @@ static netdev_tx_t hsr_dev_xmit(struct sk_buff *skb, struct net_device *dev)
 	if (master) {
 		skb->dev = master->dev;
 		skb_reset_mac_header(skb);
+		skb_reset_mac_len(skb);
 		hsr_forward_skb(skb, master);
 	} else {
 		atomic_long_inc(&dev->tx_dropped);
@@ -259,6 +260,7 @@ static struct sk_buff *hsr_init_skb(struct hsr_port *master)
 		goto out;
 
 	skb_reset_mac_header(skb);
+	skb_reset_mac_len(skb);
 	skb_reset_network_header(skb);
 	skb_reset_transport_header(skb);