mediatek: fix IPv4 address missing on interface in failsafe mode for cudy ap3000-v1

mediatek: fix IPv4 address missing on interface in failsafe mode for cudy ap3000-v1

cudy ap3000-v1 did not work correctly in failsafe mode
because the address 192.168.1.1 was missing on the eth0 inteface.
it was reachable via it's IPv6 link-local address however.
this commit fixes the issue.

Fixes: https://github.com/openwrt/openwrt/issues/20750
Signed-off-by: Martin Nadvornik <martin.nadvornik@gmx.at>
Link: https://github.com/openwrt/openwrt/pull/21172
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
(cherry picked from commit e5cd6461c905184db8f49692f931b20fec4b819e)