Route adding when creating the interface not working

Hey @wojcik91 ,

Since the 0.2.1 release, the library is not able to automatically add the route IP to the routing table.
I have to manually add the routing ip with :

`sudo ip route add 10.0.0.0/24" dev wg0` (depending on the network...)

And this way it works.

Do you have some insights about this ? Maybe some things I have to add that are not present in the server.rs right now as example ? (it may also complete the #23 )

Best,
Ange