sd_id	IN:	SD interface identifier returned by SDstart
	block_size	IN:	Size of the block in bytes

	Purpose	Sets the block size used for storing data sets with unlimited dimensions.
	Return value	Returns SUCCEED (or 0) if successful and FAIL (or -1) otherwise.
	Description	SDsetblocksize sets the block size defined in the parameter block_size for all data sets in the file. SDsetblocksize is used when creating new data sets only; it has no effect on pre-existing data sets.
		SDsetblocksize must be used after calls to SDcreate or SDselect and before the call to SDwritedata.
		The block_size parameter should be set to a multiple of the desired buffer size.

	FORTRAN	integer sfsblsz(sd_id, block_size)
		integer sd_id, block_size