Certain ZTE modems, namely: MF823. MF831, MF910, built-in modem from
MF286R, expose both CDC-ECM and RNDIS network interfaces.
They have a trait of ignoring the locally-administered MAC address
configured on the interface both in CDC-ECM and RNDIS part,
and this leads to dropping of incoming traffic by the host.
However, the workaround was only present in CDC-ECM, and MF286R
explicitly requires it in RNDIS mode.

Re-use the workaround in rndis_host as well, to fix operation of MF286R
module, some versions of which expose only the RNDIS interface. Do so by
introducing new flag, RNDIS_DRIVER_DATA_DST_MAC_FIXUP, and testing for it
in rndis_rx_fixup. This is required, as RNDIS uses frame batching, and all
of the packets inside the batch need the fixup. This might introduce a
performance penalty, because test is done for every returned Ethernet
frame.

Apply the workaround to both "flavors" of RNDIS interfaces, as older ZTE
modems, like MF823 found in the wild, report the USB_CLASS_COMM class
interfaces, while MF286R reports USB_CLASS_WIRELESS_CONTROLLER.
Suggested-by: Bjørn Mork <bjorn@mork.no>
Cc: Kristian Evensen <kristian.evensen@gmail.com>
Cc: Oliver Neukum <oliver@neukum.org>
Signed-off-by: Lech Perczak <lech.perczak@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>