DNS ALGs: DDNS support

Dynamic DNS (DDNS) support is now available in addition to the DNS standard. The main difference between DNS and DDNS is in the message format of the header section and the update message. DDNS messages are processed differently when compared to DNS messages. Message parsing is rewritten for DDNS. DDNS does NAT and NAT-PT in the query part of the message and DNS does NAT and NAT-PT in the response part of the message.