Log Message:
Update nsd to version 4.1.17.

Changes from release notes.

Features

* zone parser parses type AVC (it has TXT format).
* Fix #1272: use writev to put tcp length field
  with data for outgoing zone transfer requests.

Bugfixes

* Fix potential null pointer in nsec3 adjustment tree.
* Fix text format of deletes for CDS and CDNSKEY,
  single 0 to represent empty base64 or hex string.