Merge branch 'mlxsw-GRE-mtu-changes'

Ido Schimmel says:

====================
mlxsw: Handle changes to MTU in GRE tunnels

Petr says:

When offloading GRE tunnels, the MTU setting is kept fixed after the
initial offload even as the slow-path configuration changed. Worse: the
offloaded MTU setting is actually just a transient value set at the time
of NETDEV_REGISTER of the tunnel. As of commit ffc2b6ee4174 ("ip_gre:
fix IFLA_MTU ignored on NEWLINK"), that transient value is zero, and
unless there's e.g. a VRF migration that prompts re-offload, it stays at
zero, and all GRE packets end up trapping.

Thus, in patch #1, change the way the MTU is changed post-registration,
so that the full event protocol is observed. That way the drivers get to
see the change and have a chance to react.

In the remaining two patches, implement support for MTU change in mlxsw
driver.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>