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

goto err_free_skb if an unexpected result is returned by pskb_tirm()
in erspan_fb_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

@@ -548,7 +548,8 @@ static void erspan_fb_xmit(struct sk_buff *skb, struct net_device *dev)
 		goto err_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 err_free_skb;
 		truncate = true;
 	}