net: Fix a data-race around gro_normal_batch.

While reading gro_normal_batch, it can be changed concurrently.
Thus, we need to add READ_ONCE() to its reader.

Fixes: 323ebb61 ("net: use listified RX for handling GRO_NORMAL skbs")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Acked-by: Edward Cree <ecree.xilinx@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/gro.h

@@ -439,7 +439,7 @@ static inline void gro_normal_one(struct napi_struct *napi, struct sk_buff *skb,
 {
 	list_add_tail(&skb->list, &napi->rx_list);
 	napi->rx_count += segs;
-	if (napi->rx_count >= gro_normal_batch)
+	if (napi->rx_count >= READ_ONCE(gro_normal_batch))
 		gro_normal_list(napi);
 }