Connect to NQPTP control socket on localhost

Connect to NQPTP control socket on localhost

nqptp.c listens on "localhost", but shairport-sync connectes to the wildcard
address 0/0.  This apparently works on Linux and FreeBSD, but OpenBSD fails:

```
$ ktrace shairport-sync -v -u
[...]
         0.000038288 "ptp-utilities.c:243" *fatal error: error sending timing_peer_list to NQPTP
         0.000021868 "shairport.c:1728" emergency exit
$ kdump
[...]
  2319 shairport-sync STRU  struct sockaddr { AF_INET, 0.0.0.0:9000 }
  2319 shairport-sync RET   sendto -1 errno 51 Network is unreachable
[...]
```

Resolve and connect to "localhost" just like NQPTP does, resulting in
127.0.0.1 or ::1 as socket addresses.

This is required to run when configured `--with-airplay-2`.
Tested on OpenBSD/amd64 7.4-current with shairport-sync 2.4.3 and nqptp
1.2.5-dev cfa8315 (plus OpenBSD fixes).

I expect Linux and FreeBSD to work as before, but have not tested it.