bsc: Check for the rand and then generate a res

Check if the NAT has sent 16 bytes of RAND and if a key
has been configured in the system and then generate a
result using milenage. The milenage res will be sent and
noth the four byte GSM SRES derivation.
diff --git a/openbsc/src/osmo-bsc_nat/bsc_nat.c b/openbsc/src/osmo-bsc_nat/bsc_nat.c
index 254ea42..9837709 100644
--- a/openbsc/src/osmo-bsc_nat/bsc_nat.c
+++ b/openbsc/src/osmo-bsc_nat/bsc_nat.c
@@ -394,7 +394,7 @@
 
 static void send_id_get_response(struct bsc_msc_connection *msc_con)
 {
-	struct msgb *msg = bsc_msc_id_get_resp(0, nat->token);
+	struct msgb *msg = bsc_msc_id_get_resp(0, nat->token, NULL, 0);
 	if (!msg)
 		return;