SslHander wrap conditional direct buffer allocation

Motivation:
The SslHandler currently forces the use of a direct buffer for the input to the SSLEngine.wrap(..) operation. This allocation may not always be desired and should be conditionally done.

Modifications:
- Use the pre-existing  `wantsDirectBuffer` variable as the condition to do the conversion.

Result:
- An allocation of a direct byte buffer and a copy of data is now not required for every SslHandler wrap operation.
This sounds legit... @trustin agree ?