Prevent premptively allocating routes slice when config.yaml exists

[TimEnglart]

When you have a config file defined, but have routes unset (not included in the file), it still does not allow the F5 to set your routes. This fixes this so you have to define routes: [] in your config file in order to get the no routing functionality, while allowing you to have it unset and also have a config file for other settings, while having automatically managed routes.

Having this line allocates the slice so the later check to allocate dynamic routes fails, and it is directly assigned to later, so this allocation doesn't need to happen:

gof5/pkg/link/link.go

Lines 323 to 327 in c0f3903

	routes := cfg.Routes
	if routes == nil {
	log.Printf("Applying routes, pushed from F5 VPN server")
	routes = cfg.F5Config.Object.Routes
	}

---

Previously:
No config.yaml => F5 managed routes
Unset routes in config.yaml => No routes managed
Set routes: [] in config.yaml => No routes managed
Set routes: [1.1.1.1] in config.yaml => Only routes [1.1.1.1] are used

---

Now:
No config.yaml => F5 managed routes
Unset routes in config.yaml => F5 managed routes
Set routes: [] in config.yaml => No routes managed
Set routes: [1.1.1.1] in config.yaml => Only routes [1.1.1.1] are used