dirmngr: Fix libdns with 127.0.0.1.
* dirmngr/dns.c (dns_so_check): Ifdef-out Linux specific code. Remove retrying udp_connect_retry when ECONNREFUSED.
- Fixes-commit: bcdbf8b8ebe9d61160e0b007dabe1b6462ffbc93
- GnuPG-bug-id: T4021
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>