channels/Common.java allocates an extra ByteBuffer unnecessarily in read and write

[athanatos]

As far as I can tell, jnr-ffi is fine with array-backed or direct buffers, so we can avoid the extra allocation in those cases.

[huntc]

Amazing, I was just about to raise this same issue!

[gregw]

Note also that the copy in write is implemented incorrectly for asynchronous writes, as it consumes the passed buffer even if not all of the data is written. See #50

[CAFEBABE88]

will this lead to memory leak issues？
I use jnr-unixsocket as my java process IPC lib with other processes, I foud the off-heap memory consumption is very high, but I didn't allocate any direct bytebuffer in my java code.