Merge branch 'macsec-offload' into next

Antoine Tenart  says:

====================

This series adds support for selecting and reporting the offloading mode
of a MACsec interface. Available modes are for now 'off' and 'phy',
'off' being the default when an interface is created. Modes are not only
'off' and 'on' as the MACsec operations can be offloaded to multiple
kinds of specialized hardware devices, at least to PHYs and Ethernet
MACs. The later isn't currently supported in the kernel though.

The first patch adds support for reporting the offloading mode currently
selected for a given MACsec interface through the `ip macsec show`
command:

   # ip macsec show
   18: macsec0: protect on validate strict sc off sa off encrypt on send_sci on end_station off scb off replay off
       cipher suite: GCM-AES-128, using ICV length 16
       TXSC: 3e5035b67c860001 on SA 0
           0: PN 1, state on, key 00000000000000000000000000000000
       RXSC: b4969112700f0001, state on
           0: PN 1, state on, key 01000000000000000000000000000000
->     offload: phy
   19: macsec1: protect on validate strict sc off sa off encrypt on send_sci on end_station off scb off replay off
       cipher suite: GCM-AES-128, using ICV length 16
       TXSC: 3e5035b67c880001 on SA 0
           1: PN 1, state on, key 00000000000000000000000000000000
       RXSC: b4969112700f0001, state on
           1: PN 1, state on, key 01000000000000000000000000000000
->     offload: off

The second patch allows an user to change the offloading mode at runtime
through a new subcommand, `ip macsec offload`:

  # ip macsec offload macsec0 phy
  # ip macsec offload macsec0 off

If a mode isn't supported, `ip macsec offload` will report an issue
(-EOPNOTSUPP).

Giving the offloading mode when a macsec interface is created was
discussed; it is not implemented in this series. It could come later
on, when needed, as we'll still want to support updating the offloading
mode at runtime (what's implemented in this series).
====================

Signed-off-by: David Ahern <dsahern@gmail.com>