ieee802154: fix skb get fc on big endian

This patch fixes ieee802154_get_fc_from_skb function on big endian
machines. The function get_unaligned_le16 converts the byte order to
host byte order but we want to keep the byte order like in mac header.
Signed-off-by: Alexander Aring <aar@pengutronix.de>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

include/net/mac802154.h

@@ -247,6 +247,8 @@ struct ieee802154_ops {
  */
 static inline __le16 ieee802154_get_fc_from_skb(const struct sk_buff *skb)
 {
+	__le16 fc;
+
 	/* check if we can fc at skb_mac_header of sk buffer */
 	if (unlikely(!skb_mac_header_was_set(skb) ||
 		     (skb_tail_pointer(skb) - skb_mac_header(skb)) < 2)) {
@@ -254,7 +256,8 @@ static inline __le16 ieee802154_get_fc_from_skb(const struct sk_buff *skb)
 		return cpu_to_le16(0);
 	}
 
-	return get_unaligned_le16(skb_mac_header(skb));
+	memcpy(&fc, skb_mac_header(skb), IEEE802154_FC_LEN);
+	return fc;
 }
 
 /**