net: macsec: Add missing documentation for 'gro_cells'

commit 0be2e9436bbe1dfad3939938d32e3e85c5f56a49 from
git@git.assembla.com:cavium/WindRiver.linux.git

Fixes the following W=1 kernel build warning(s):

 drivers/net/macsec.c:113: warning: Function parameter or member 'gro_cells' not described in 'macsec_dev'

Change-Id: I406b57dcf1781b4c28f0389f49bb57defafbf531
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20201102114512.1062724-26-lee.jones@linaro.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Subbaraya Sundeep <sbhatta@marvell.com>
Reviewed-on: https://sj1git1.cavium.com/c/IP/SW/kernel/linux/+/82832


Tested-by: sa_ip-sw-jenkins <sa_ip-sw-jenkins@marvell.com>
Reviewed-by: Sunil Kovvuri Goutham <sgoutham@marvell.com>
Signed-off-by: Wenlin Kang <wenlin.kang@windriver.com>