macsec: not handle MKA packets in case of offload

MKA packets (ETH_P_PAE) are defenitelly not encrypted so
they should not be in macsec interface.

Change-Id: Ie1619471948e2f78a961c712bdfcc56a87d90c57
Signed-off-by: Dmitry Bogdanov <dbogdanov@marvell.com>
Git-commit: 797e7df618e11807ca7f4eac7c84ad4296cdf0e1
Git-repo: https://github.com/aquantia/linux-4.14-atlantic-forwarding


Signed-off-by: Jinesh K. Jayakumar <jineshk@codeaurora.org>