CVE-2021-47560

In the Linux kernel, the following vulnerability has been resolved: mlxsw:
spectrum: Protect driver from buggy firmware When processing port up/down
events generated by the device’s firmware, the driver protects itself from
events reported for non-existent local ports, but not the CPU port (local
port 0), which exists, but lacks a netdev. This can result in a NULL
pointer dereference when calling netif_carrier_{on,off}(). Fix this by
bailing early when processing an event reported for the CPU port. Problem
was only observed when running on top of a buggy emulator.