NetworkManager: Disable ifupdown plugin

Ifupdown is used on the Debian and Ubuntu distributions, and reads Ethernet and
Wi-Fi connections from /etc/network/interfaces. It's not needed for
Oniro.

Closes: https://booting.oniroproject.org/distro/oniro/-/issues/134



Signed-off-by: Pavel Zhukov <pavel.zhukov@huawei.com>