OpenWRT on the WNDAP6x0 refuses to sysupgrade to itself
due to a compat_version imbalance. The Image is generated
with version 2.0, but the uci-defaults says that it needs
to be at 3.0 for the device.

Fix this by downgrading WNDAP6x0 05_fix-compat-version's
values back to 2.0 so it matches what we use.

Fixes: 5815884c ("apm821xx: migrate to DSA")
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>