Add a choice for setting default routelist in GUI

[jyzhiyu]

Feature discussion: Add a choice for setting default route-list

Today I updated Openconnect-GUI to 1.5.3, and I found this new version add a default route:

Net target 0.0.0.0 Mask code 0.0.0.0

I checked the vpnc-script.js and found the diff from 1.5.2 to 1.5.3

// How to add the default internal route
// -1 - Do not touch default route (but do other necessary route setups)
// 0 - As interface gateway when setting properties
// 1 - As a 0.0.0.0/0 route with a lower metric than the default route
// 2 - As 0.0.0.0/1 + 128.0.0.0/1 routes (override the default route cleanly)
if (env("REDIRECT_GATEWAY_METHOD")) {
	var REDIRECT_GATEWAY_METHOD = env("REDIRECT_GATEWAY_METHOD");
} else {
	var REDIRECT_GATEWAY_METHOD = -1;
}

REDIRECT_GATEWAY_METHOD is set to '0' in new version and was set to '-1' in old version.

Many people want to use option '0', but in same time many people want to keep the option '-1'. That I hope GUI could add a feature to set this option.