This commit adds support for the EDNS Report-Channel option,
which is returned in authoritative responses when EDNS is in use.
"send-report-channel" sets the Agent-Domain value that will be
included in EDNS Report-Channel options. This is configurable at
the options/view level; the value is a DNS name. Setting the
Agent-Domain to the root zone (".") disables the option.
When this value has been set, incoming queries matchng the form
_er.<qtype>.<qname>.<extended-error-code>._er.<agent-domain>/TXT
will be logged to the dns-reporting-agent channel at INFO level.
(Note: error reporting queries will only be accepted if sent via
TCP or with a good server cookie. If neither is present, named
returns BADCOOKIE to complete the DNS COOKIE handshake, or TC=1
to switch the client to TCP.)
ac1c60d87e