net: usb: qmi_wwan: fix memory leak for not ip packets

BugLink: https://bugs.launchpad.net/bugs/2083656

[ Upstream commit 7ab107544b777c3bd7feb9fe447367d8edd5b202 ]

Free the unused skb when not ip packets arrive.

Fixes: c6adf77953 ("net: usb: qmi_wwan: add qmap mux protocol support")
Signed-off-by: Daniele Palmas <dnlplm@gmail.com>
Acked-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Koichiro Den <koichiro.den@canonical.com>
Signed-off-by: Roxana Nicolescu <roxana.nicolescu@canonical.com>

drivers/net/usb/qmi_wwan.c

@@ -201,6 +201,7 @@ static int qmimux_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
 			break;
 		default:
 			/* not ip - do not know what to do */
+			kfree_skb(skbn);
 			goto skip;
 		}