Correct constant: NET_SFTP_BLOCK_DEVICE -> NET_SFTP_TYPE_BLOCK_DEVICE
Merge pull request #487 from bantu/fix-486

Correct constant: NET_SFTP_BLOCK_DEVICE -> NET_SFTP_TYPE_BLOCK_DEVICE

* bantu/fix-486:
  Correct constant: NET_SFTP_BLOCK_DEVICE -> NET_SFTP_TYPE_BLOCK_DEVICE