issue #476: fixed zero flag not being zeroed + added test

src/knot/nameserver/internet.c

@@ -219,6 +219,9 @@ static int put_answer(knot_pkt_t *pkt, uint16_t type, struct query_data *qdata)
}
break;
}
+	/* RFC 1035 page 26: Z     Reserved for future use.  Must be zero in all queries
+		and responses. */
+	knot_wire_clear_z(pkt->wire);
return ret;
}