compression plugin compress level validation

Hey guys, original discussion started here (for reference): https://github.com/kronosnet/kronosnet/pull/128 int knet_handle_compress(knet_handle_t knet_h, struct knet_handle_compress_cfg *knet_handle_compress_cfg); Where knet_handle_compress_cfg contains int compress_level. As you can see from libknet.h and relative code, we try (too hard) to validate the values for compress_level. Feri had a proper concern about applying incorrect filtering and I agree that it is already becoming complex to maintain a matrix of valid values, per plugin, per plugin-version, and whatever combination. AFAIR all plugins accept an int value for compress_level so from that perspective it shouldn´t be too much of a problem (aka no API/ABI changes). Historically, the reason why I added the validation was lzo2, that presents a rather unusual compress configuration vs all other plugins (as you can see). I think Feri´s suggestion to drop the filter completely might be too much, instead, after thinking a bit, it might be perfectly reason to change the internals of val_level to try and compress a small buffer to test that the value is good. The val_level is used only at configuration time, so it´s not too expensive to compress one small data chunk for validation and it would remove the whole hardcoded filter of different compress_levels. For special plugins like lzo2, I think it´s important we improve the logging at configuration time to make sure users at least warned of supported values (as you can see each values map to a specific lzo2 API call to compress). wdyt? Fabio