network: change UseGateway= default to UseRoutes= setting

network: change UseGateway= default to UseRoutes= setting

Anyone previously using the UseRoutes=false parameter expected their
dhcp4-provided gateway route to be ignored, as well.  However, with
the introduction of the UseGateway= parameter, this is no longer true.

In order to keep backwards compatibility, this sets the UseGateway=
default value to whatever UseRoutes= has been set to.

(cherry picked from commit 589397a27759bd650b3674029cb0ef73347c913b)

Gbp-Pq: Name network-change-UseGateway-default-to-UseRoutes-setting.patch