net: usb: qmi_wwan: Set DTR quirk for MR400

LTE module MR400 embedded in TL-MR6400 v4 requires DTR to be set.

Signed-off-by: Filip Moc <dev@moc6.cz>
Acked-by: Bjørn Mork <bjorn@mork.no>
Link: https://lore.kernel.org/r/20201117173631.GA550981@moc6.cz


Signed-off-by: Jakub Kicinski <kuba@kernel.org>