NFSv4.2 WRITE_SAME support

[dfshelton]

Please add support for the NFSv4.2 WRITE_SAME request, so repeated data (pattern fill, fill blocks with 0x00/0xff/0xdd ...) only need one request.

SMB3.0 already supports this on Windows, giving the Windows platform a huge advantage over NFSv4, for applications like big data or databases.