pass sizeof(struct sockaddr_in) for AF_INET instead of always using
sizeof(struct sockaddr_in6). also skip getnameinfo entirely for
non-matching interfaces rather than calling it for every entry.

Fixes coding style. Formatting commits suck, incoherent coding style
sucks more.
https://suckless.org/coding_style/

Except stated otherwise in comment.

Fixes coding style. Formatting commits suck, incoherent coding style
sucks more.
https://suckless.org/coding_style/

this gives the compiler a chance to check weather the prototype and
definiton matches or not, which would catch issues like 3c47701.

 - Remove <errno.h> because related functions are in util.c now
 - Remove corresponding <string.h> if not used otherwise

free the interface list before returning from the function