sua: call conn_disconnect() in sua_disconnect_req()

disconnect is not a class3/4 operation. We simply generate + send the
DISCONNECT.ind message to the remote side and drop all local state about the
connection.

Change-Id: I4e336f9dfd4ebd0122cd9e5a70db3d05e9dc1764

src/sua.c

@@ -548,6 +548,7 @@ static int sua_disconnect_req(struct osmo_sccp_link *link, struct osmo_scu_prim
 	xua_msg_free(xua);
 
 	conn_state_set(conn, S_DISCONN_PEND);
+	conn_destroy(conn);
 
 	return sua_link_send(link, outmsg);
 }