Fix a regression caused by 73dfd7c01b49aca006a34cc48197dee3fc360af1

Motivation:

73dfd7c01b49aca006a34cc48197dee3fc360af1 introduced various test
failures because:

- EpollSocketChannel.doWrite() raised a NullPointerException when
  notifying the write progress.
- ChannelOutboundBuffer.nioBuffers() did not expand the internal array
  when the pending entries contained more than 1024 buffers, dropping
  the remainder.

Modifications:

- Fix the NPE in EpollSocketChannel by removing an unnecessary progress
  update
- Expand the thread-local buffer array if there is not enough room,
  which was the original behavior dropped by the offending commit

Result:

Regression is gone.