[PATCH] fix dhcp template generation

The dhcp template generation is broken when there is no dns-name for interfaces set. The attached patch fixes this problem and does some cleanup to the code. Also the entries are now named with the system record name and interface instead of generic<idx>. This makes debugging the template easier. Peter This e-mail and any attachment is for authorised use by the intended recipient(s) only. It may contain proprietary material, confidential information and/or be subject to legal privilege. It should not be copied, disclosed to, retained or used by, any other party. If you are not an intended recipient then please promptly delete this e-mail and any attachment and all copies and inform the sender. Thank you.