net: introduce the MACSEC netdev feature

This patch introduce a new netdev feature, which will be used by drivers
to state they can perform MACsec transformations in hardware.

Change-Id: I915bb217f48b323219d90e72c17d061b33802c9b
Signed-off-by: Antoine Tenart <antoine.tenart@bootlin.com>
Git-commit: aab2134205547805eb73fc4550601e087bbac1f8
Git-repo: https://github.com/aquantia/linux-4.14-atlantic-forwarding


[jineshk@codeaurora.org: Fix trivial merge conflicts]
Signed-off-by: Jinesh K. Jayakumar <jineshk@codeaurora.org>