ethtool: Improve explanation of the two arrays following struct ethtool_rxfh

The use of two variable-length arrays is unusual so deserves a bit
more explanation.
Signed-off-by: NBen Hutchings <ben@decadent.org.uk>

include/uapi/linux/ethtool.h

@@ -850,16 +850,17 @@ struct ethtool_rxfh_indir {
  * struct ethtool_rxfh - command to get/set RX flow hash indir or/and hash key.
  * @cmd: Specific command number - %ETHTOOL_GRSSH or %ETHTOOL_SRSSH
  * @rss_context: RSS context identifier.
- * @indir_size: On entry, the array size of the user buffer, which may be zero,
- *		or (for %ETHTOOL_SRSSH), %ETH_RXFH_INDIR_NO_CHANGE.
- *		On return from %ETHTOOL_GRSSH, the array size of the hardware
- *		indirection table.
- * @key_size:	On entry, the array size of the user buffer in bytes,
- *		which may be zero.
- *		On return from %ETHTOOL_GRSSH, the size of the RSS hash key.
+ * @indir_size: On entry, the array size of the user buffer for the
+ *	indirection table, which may be zero, or (for %ETHTOOL_SRSSH),
+ *	%ETH_RXFH_INDIR_NO_CHANGE.  On return from %ETHTOOL_GRSSH,
+ *	the array size of the hardware indirection table.
+ * @key_size: On entry, the array size of the user buffer for the hash key,
+ *	which may be zero.  On return from %ETHTOOL_GRSSH, the size of the
+ *	hardware hash key.
  * @rsvd:	Reserved for future extensions.
  * @rss_config: RX ring/queue index for each hash value i.e., indirection table
- *		of size @indir_size followed by hash key of size @key_size.
+ *	of @indir_size __u32 elements, followed by hash key of @key_size
+ *	bytes.
  *
  * For %ETHTOOL_GRSSH, a @indir_size and key_size of zero means that only the
  * size should be returned.  For %ETHTOOL_SRSSH, an @indir_size of