fix not execute unit test in transport-native-unix-common-tests module
Motivation:
- Commit 047da11 introduced an bug for still copy byteBuf for composed of n(n <= IOV_MAX) NIO direct buffers
- Commit 3c4dfed add UnixChannelUtilTest in transport-native-unix-common-tests module, but not execute in maven compile
as issue #6825, #6870
Modifications:
- modified UnixChannelUtil#isBufferCopyNeededForWrite(ByteBuf), and UnixChannelUtilTest
- move UnixChannelUtilTest into transport-native-unix-common module, and add packet scope method UnixChannelUtil#isBufferCopyNeededForWrite(ByteBuf, int)
Result:
- no copy byteBuf for composed of n(n <= IOV_MAX) NIO direct buffers
- auto execute unit tests in UnixChannelUtilTest and it is easier to mock IOV_MAX
