Motivation:
It is not uncommon to run Netty on OS X without the specific
`MacOSDnsServerAddressStreamProvider`. The current log message is too
verbose because it prints a full stack trace on the console while a
simple logging message would have been enough.
Modifications:
- Print a `WARN` message when `MacOSDnsServerAddressStreamProvider`
class is not found;
- Print a `ERROR` message with a stack trace when the class was found
but could not be loaded due to some other reasons;
Result:
Less noise in logs.
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