networking.service should have far less sleeping time

Many networking service is blocked for this service: /lib/systemd/system/networking.service.

For most of PC set "iface enp3s0 inet dhcp" in /etc/network/interfaces, and when they are using wireless network access without wired network plugged. Currently they have to wait for 5 minute of their booting time. I think 3-5 sec is reasonable and 0 sec is the best.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ifupdown 0.8.16ubuntu2 [modified: lib/systemd/system/networking.service]
ProcVersionSignature: Ubuntu 4.13.0-32.35-generic 4.13.13
Uname: Linux 4.13.0-32-generic x86_64
ApportVersion: 2.20.8-0ubuntu8
Architecture: amd64
CurrentDesktop: MATE
Date: Mon Feb 12 01:56:56 2018
SourcePackage: ifupdown
UpgradeStatus: No upgrade log present (probably fresh install)