net: ethtool: Document get_rxfh_context and set_rxfh_context ethtool ops

ethtool ops get_rxfh_context and set_rxfh_context are used to create,
remove and access parameters associated to RSS contexts, in a similar
fashion to get_rxfh and set_rxfh.

Add a small descritopn of these callbacks in the struct ethtool_ops doc.
Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/ethtool.h

@@ -260,6 +260,15 @@ bool ethtool_convert_link_mode_to_legacy_u32(u32 *legacy_u32,
  *	will remain unchanged.
  *	Returns a negative error code or zero. An error code must be returned
  *	if at least one unsupported change was requested.
+ * @get_rxfh_context: Get the contents of the RX flow hash indirection table,
+ *	hash key, and/or hash function assiciated to the given rss context.
+ *	Returns a negative error code or zero.
+ * @set_rxfh_context: Create, remove and configure RSS contexts. Allows setting
+ *	the contents of the RX flow hash indirection table, hash key, and/or
+ *	hash function associated to the given context. Arguments which are set
+ *	to %NULL or zero will remain unchanged.
+ *	Returns a negative error code or zero. An error code must be returned
+ *	if at least one unsupported change was requested.
  * @get_channels: Get number of channels.
  * @set_channels: Set number of channels.  Returns a negative error code or
  *	zero.