vfs: Add flags and xferlen args to SMB_VFS_OFFLOAD_READ_RECV

vfs: Add flags and xferlen args to SMB_VFS_OFFLOAD_READ_RECV

We missed these values which follow from MS-FSCC 2.3.80 “FSCTL_OFFLOAD_READ
Reply”:

  Flags (4 bytes):

    A 32-bit unsigned integer that indicates which flags were returned for this
    operation. Possible values for the flags follow. All unused bits are reserved
    for future use, SHOULD be set to 0, and MUST be ignored.

    OFFLOAD_READ_FLAG_ALL_ZERO_BEYOND_CURRENT_RANGE (0x00000001)
    => The data beyond the current range is logically equivalent to zero.

  TransferLength (8 bytes):

    A 64-bit unsigned integer that contains the amount, in bytes, of data that the
    Token logically represents. This value indicates a contiguous region of the
    file from the beginning of the requested offset in the FileOffset field in the
    FSCTL_OFFLOAD_READ_INPUT data element (section 2.3.79). This value can be
    smaller than the CopyLength field specified in the FSCTL_OFFLOAD_READ_INPUT
    data element, which indicates that less data was logically
    represented (logically read) with the Token than was requested. The value of
    this field MUST be greater than 0x0000000000000000 and MUST be aligned to a
    logical sector boundary on the volume.

As we currently only implement COPY_CHUNK over the OFFLOAD VFS interface, the
VFS COPY_CHUNK backend in vfs_default just sets both values to 0 and they are
unused in the SMB frontend.

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>