staging: rtl8723au: OnAction23a(): Use struct ieee80211_mgmt instead of hardcoded offsets

OnAction23a(struct rtw_adapter *padapter, struct recv_frame *precv_frame)

{

	int i;

	unsigned char	category;

	u8 category;

	struct action_handler *ptable;

	unsigned char	*frame_body;

	struct sk_buff *skb = precv_frame->pkt;

	u8 *pframe = skb->data;

	frame_body = (unsigned char *)

		(pframe + sizeof(struct ieee80211_hdr_3addr));

	struct ieee80211_mgmt *mgmt = (struct ieee80211_mgmt *) skb->data;

	category = frame_body[0];

	category = mgmt->u.action.category;

	for (i = 0;

	     i < sizeof(OnAction23a_tbl) / sizeof(struct action_handler); i++) {