net/macsec: Move some code for sharing with various drivers that implements offload

commit 0353cbe6e81340dc42dbdd82048e84d1cc0bc554 from
git@git.assembla.com:cavium/WindRiver.linux.git

Move some MACsec infrastructure like defines and functions,
in order to avoid code duplication for future drivers which
implements MACsec offload.

Change-Id: I03121c3238a18b912d821a3fc63b1ea4b4d26677
Signed-off-by: Lior Nahmanson <liorna@nvidia.com>
Reviewed-by: Raed Salem <raeds@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Ben Ben-Ishay <benishay@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Subbaraya Sundeep <sbhatta@marvell.com>
Reviewed-on: https://sj1git1.cavium.com/c/IP/SW/kernel/linux/+/92154


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>