Bind to a link-local IPv6-address

I believe, in order to bind to a link-local IPv6 address, either the application needs to find the interface by iterating through all of them, what is does not do at the time:
```
./dnsproxy -l fe80::61*6f
[fatal] cannot start the DNS proxy due to listening to udp socket: listen udp [fe80::61*6f]:53: bind: invalid argument
```
or it must accept the interface ID, which it can't parse at the moment:
```
./dnsproxy -l fe80::61*6f%eth0
[fatal] cannot parse fe80::61*6f%eth0
```
Could you please extend the code to enable binding to link-local IPv6 addresses?