ipv4: ip_gre: fix return value check in erspan_xmit()

goto free_skb if an unexpected result is returned by pskb_tirm()
in erspan_xmit().
Signed-off-by: Yuanjun Gong <ruc_gongyuanjun@163.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/ip_gre.c

@@ -690,7 +690,8 @@ static netdev_tx_t erspan_xmit(struct sk_buff *skb,
 		goto free_skb;
 
 	if (skb->len > dev->mtu + dev->hard_header_len) {
-		pskb_trim(skb, dev->mtu + dev->hard_header_len);
+		if (pskb_trim(skb, dev->mtu + dev->hard_header_len))
+			goto free_skb;
 		truncate = true;
 	}