modules/dns64: bad expectation of ffi.copy semantics

the copy doesn't take cdata length into account, but measures string len

refs #43

daemon/lua/kres.lua

@@ -334,7 +334,7 @@ ffi.metatype( knot_pkt_t, {
 		end, 
 		begin = function (pkt, section) return knot.knot_pkt_begin(pkt, section) end,
 		put = function (pkt, owner, ttl, rclass, rtype, rdata)
-			return C.kr_pkt_put(pkt, owner, ttl, rclass, rtype, rdata, string.len(rdata))
+			return C.kr_pkt_put(pkt, owner, ttl, rclass, rtype, rdata, #rdata)
 		end,
 		clear = function (pkt) return C.kr_pkt_recycle(pkt) end,
 		question = function(pkt, qname, qclass, qtype)

modules/dns64/dns64.lua

@@ -28,7 +28,7 @@ mod.layer = {
 				local rr = answer[i]
 				-- Synthesise AAAA from A
 				if rr.type == kres.type.A then
-					ffi.copy(addr_buf, mod.proxy)
+					ffi.copy(addr_buf, mod.proxy, 16)
 					ffi.copy(addr_buf + 12, rr.rdata, 4)
 					req.answer:put(rr.owner, rr.ttl, rr.class, kres.type.AAAA, ffi.string(addr_buf, 16))
 				end