net: add missing net_device::xdp_zc_max_segs description

Cited commit under 'Fixes' tag introduced new member to struct
net_device without providing description of it - fix it.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Closes: https://lore.kernel.org/all/20230720141613.61488b9e@canb.auug.org.au/
Fixes: 13ce2da ("xsk: add new netlink attribute dedicated for ZC max frags")
Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Tested-by: Simon Horman <simon.horman@corigine.com> # build-tested
Link: https://lore.kernel.org/r/20230721145808.596298-1-maciej.fijalkowski@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/linux/netdevice.h

@@ -2043,6 +2043,8 @@ enum netdev_ml_priv_type {
  *			receive offload (GRO)
  * 	@gro_ipv4_max_size:	Maximum size of aggregated packet in generic
  * 				receive offload (GRO), for IPv4.
+ *	@xdp_zc_max_segs:	Maximum number of segments supported by AF_XDP
+ *				zero copy driver
  *
  *	@dev_addr_shadow:	Copy of @dev_addr to catch direct writes.
  *	@linkwatch_dev_tracker:	refcount tracker used by linkwatch.