Outgoing-interface config option

Hello, I'm using libunbound in my application (proxy server), and I
need to configure libunbound with specific outgoing interface for DNS
requests.
I've wrote this patch (tested with libunbound 1.4.9 and 1.4.12):

Index: unbound-1.4.12/util/config_file.c

Hi Nicholas,

Thanks for the patch, applied it and fixed up memory leak in patch (if
alloc fails, of dupped strs).

I have turned the patch into this:
Index: util/config_file.c