Draft: Configure with --enable-dnstap by default
All platforms but OpenBSD have fstrm and protobuf-c in their repositories and
DNSTAP can be tested there. The DNSTAP testing reach can be broadened by making the --enable-dnstap option the default and disabling DNSTAP where necessary or suitable. For the sake of testing in Linux
environments where DNSTAP dependencies are not present, --disable-dnstap
was added to Ubuntu Xenial job.
fstrm and protobuf-c need to be added to few CI images. images!101 needs to be merged first.