gnrc_sock_dns: Move DNS server end point to implementation

sys/net/application_layer/dns/dns.c

@@ -28,6 +28,9 @@
 /* min domain name length is 1, so minimum record length is 7 */
 #define DNS_MIN_REPLY_LEN   (unsigned)(sizeof(sock_dns_hdr_t ) + 7)
 
+/* global DNS server UDP endpoint */
+sock_udp_ep_t sock_dns_server;
+
 static ssize_t _enc_domain_name(uint8_t *out, const char *domain_name)
 {
     /*

tests/gnrc_sock_dns/main.c

@@ -35,9 +35,6 @@
 #define DNS_SERVER  "[2001:db8::1]:53"
 #endif
 
-/* global DNS server UDP endpoint */
-sock_udp_ep_t sock_dns_server;
-
 /* import "ifconfig" shell command, used for printing addresses */
 
 extern int _gnrc_netif_config(int argc, char **argv);