Support for disabling waffles runtime

All waffles will now support being en/disabled during runtime through a header
X_WAFFLEHAUS_<classname_uppercase>_ENABLED.

Similarly they support having themselves toggled between testing/not testing
with X_WAFFLEHAUS_<classname_uppercase>_TESTING.

Also discovered some terrible testing issues with dns_filter, and cleaned up
some of the lame true value tuples.