Update GlusterFileChannel.java

while i write 100mb to gluster server, the written value is file.length,byteBuffer.position >= byteBuffer.limit,cause written>limit,(limit's initial value is 8192)throws  the illegalargumentexception about bytebuffer. after fix bug,each call return the buffer.size(),and while call byteBuffer.get() ,the position is automatically forward buf.length size.maybe do not used the method byteBufffer.position() works fine.