net: usb: cdc_mbim: add flag FLAG_SEND_ZLP

BugLink: https://bugs.launchpad.net/bugs/1777063

[ Upstream commit 9f7c7283 ]

Testing Telit LM940 with ICMP packets > 14552 bytes revealed that
the modem needs FLAG_SEND_ZLP to properly work, otherwise the cdc
mbim data interface won't be anymore responsive.
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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

drivers/net/usb/cdc_mbim.c

@@ -593,7 +593,7 @@ static const struct driver_info cdc_mbim_info_zlp = {
  */
 static const struct driver_info cdc_mbim_info_ndp_to_end = {
 	.description = "CDC MBIM",
-	.flags = FLAG_NO_SETINT | FLAG_MULTI_PACKET | FLAG_WWAN,
+	.flags = FLAG_NO_SETINT | FLAG_MULTI_PACKET | FLAG_WWAN | FLAG_SEND_ZLP,
 	.bind = cdc_mbim_bind,
 	.unbind = cdc_mbim_unbind,
 	.manage_power = cdc_mbim_manage_power,