Strict mode was introduced to support "one-shot" queries (described in
RFC6762/sec5.1) that are sent by lwip or dig. It was incorrectly assumed
that responding to such queries violates the spec, as we have to repeat
queries in responces, which is forbidden in RFC6762/sec6. It is however
required to repeat query fields according to the Section 6.7. Legacy
Unicast Responses: "it MUST repeat the query ID and the question
given in the query message."
Strict mode was hardcoded in private header file, but it's useful for
users to enable/disable it depending on the mdns library they are using.
e.g. Avahi might not resolve the non-strict answers.
* Original commit: espressif/esp-idf@0eee31546d
