Core: guard use of AI_ADDRCONFIG.

Some systems (notably NetBSD and OpenBSD) lack AI_ADDRCONFIG support.

Reported by Piotr Sikora.

src/core/ngx_inet.c

diff --git a/src/core/ngx_inet.c b/src/core/ngx_inet.c
index bb03720..0792d6e 100644
--- a/src/core/ngx_inet.c
+++ b/src/core/ngx_inet.c
@@ -963,7 +963,9 @@
     ngx_memzero(&hints, sizeof(struct addrinfo));
     hints.ai_family = AF_UNSPEC;
     hints.ai_socktype = SOCK_STREAM;
+#ifdef AI_ADDRCONFIG
     hints.ai_flags = AI_ADDRCONFIG;
+#endif
 
     if (getaddrinfo((char *) host, NULL, &hints, &res) != 0) {
         u->err = "host not found";