wifi: wlcore: ensure skb headroom before skb_push

This avoids occasional skb_under_panic Oops from wl1271_tx_work. In this case, headroom is
less than needed (typically 110 - 94 = 16 bytes).

Signed-off-by: Peter Astrand <astrand@lysator.liu.se>
Link: https://patch.msgid.link/097bd417-e1d7-acd4-be05-47b199075013@lysator.liu.se
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

Author: astrand

drivers/net/wireless/ti/wlcore/tx.c

@@ -207,6 +207,11 @@ static int wl1271_tx_allocate(struct wl1271 *wl, struct wl12xx_vif *wlvif,
 	total_blocks = wlcore_hw_calc_tx_blocks(wl, total_len, spare_blocks);
 
 	if (total_blocks <= wl->tx_blocks_available) {
+		if (skb_headroom(skb) < (total_len - skb->len) &&
+		    pskb_expand_head(skb, (total_len - skb->len), 0, GFP_ATOMIC)) {
+			wl1271_free_tx_id(wl, id);
+			return -EAGAIN;
+		}
 		desc = skb_push(skb, total_len - skb->len);
 
 		wlcore_hw_set_tx_desc_blocks(wl, desc, total_blocks,