'sriov_drivers_autoprobe' was added in kernel 4.12. With previous
kernel versions NM is currently unable to set any SR-IOV parameter
because it tries to read 'sriov_drivers_autoprobe' which doesn't
exist, assumes that current value is -1 and tries to change it,
failing.
When the file doesn't exist, drivers are automatically probed so we
can assume the value is 1. In this way NM is able to activate a
connection with sriov.autoprobe-drivers=1 (the default) even on older
kernel versions.
Fixes: 1e41495d9a ('platform: sriov: write new values when we can't read old ones')
https://bugzilla.redhat.com/show_bug.cgi?id=1695093
8698f512d7