doc: add method links in dns.markdown
doc: add method links in dns.markdown

Added links to referenced methods.

PR-URL: https://github.com/nodejs/node/pull/3196
Reviewed-By: Roman Reiss <b1c1d8736f20db3fb6c1c66bb1455ed43909f0d8@silverwind.io>>

dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node