net: ethtool: Add missing kernel doc for FEC parameters

While adding support for ethtool::get_fecparam and set_fecparam, kernel
doc for these functions was missed, add those.

Fixes: 1a5f3da ("net: ethtool: add support for forward error correction modes")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Roopa Prabhu <roopa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/ethtool.h

@@ -310,6 +310,8 @@ bool ethtool_convert_link_mode_to_legacy_u32(u32 *legacy_u32,
  *	fields should be ignored (use %__ETHTOOL_LINK_MODE_MASK_NBITS
  *	instead of the latter), any change to them will be overwritten
  *	by kernel. Returns a negative error code or zero.
+ * @get_fecparam: Get the network device Forward Error Correction parameters.
+ * @set_fecparam: Set the network device Forward Error Correction parameters.
  *
  * All operations are optional (i.e. the function pointer may be set
  * to %NULL) and callers must take this into account.  Callers must