net: macsec: add nla support for changing the offloading selection

MACsec offloading to underlying hardware devices is disabled by default
(the software implementation is used). This patch adds support for
changing this setting through the MACsec netlink interface. Many checks
are done when enabling offloading on a given MACsec interface as there
are limitations (it must be supported by the hardware, only a single
interface can be offloaded on a given physical device at a time, rules
can't be moved for now).

Change-Id: Ia0b0898e7972f24e79eefcd65ff480ac819a4bb9
Signed-off-by: Antoine Tenart <antoine.tenart@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Git-commit: dcb780fb279514f268826f2e9f4df3bc75610703
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Karthik Rudrapatna <quic_krudrapa@quicinc.com>