PHP checkdnsrr* function does not work on either php5 or php7 packages

alpine:~# php5 -r "echo checkdnsrr('shouldntbevalid.com','MX') ? 'valid' : 'invalid';"
valid

alpine:~# php7 -r "echo checkdnsrr('shouldntbevalid.com','MX') ? 'valid' : 'invalid';"
valid

Expected return value should “invalid”.

• http://php.net/manual/en/function.checkdnsrr.php

(from redmine: issue id 7392, created on 2017-06-07)