Use SOCK_DNS extension on socket on OpenBSD (#659)

This patch added the `SOCK_DNS` flag when running on OpenBSD. Allowing a reduced set of `pledge(2)` promises. Before this patch. The "stdio rpath inet" promises must be used in order to resolve any records. After the patch inet can be replaced with dns which only allows communication on destination port 53, instead of on all ports.

Side note: I checked the OpenBSD kernel source code. Even though the socket document says the DNS port (typically 53)., The OpenBSD 7.4 kernel only allows 53. 

Fix By: Martin Chang (@marty1885)

src/lib/ares__socket.c

@@ -253,6 +253,11 @@ ares_status_t ares__open_connection(ares_channel_t      *channel,
   struct server_connection *conn;
   ares__llist_node_t       *node;
   int                       type = is_tcp ? SOCK_STREAM : SOCK_DGRAM;
+#ifdef __OpenBSD__
+  if((is_tcp && server->tcp_port == 53) || (!is_tcp && server->udp_port == 53)) {
+    type |= SOCK_DNS;
+  }
+#endif
 
   switch (server->addr.family) {
     case AF_INET: