selftests: extract common functions in ethtool-common.sh

Factor out some useful functions so that they can be reused
by other ethtool-netdevsim scripts.

Signed-off-by: Antonio Cardace <acardace@redhat.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

netdevsim: fix duplicated debugfs directory

The "ethtool" debugfs directory holds per-netdev knobs, so move
it from the device instance directory to the port directory.

This fixes the following warning when creating multiple ports:

debugfs: Directory 'ethtool' with parent 'netdevsim1' already present!

Fixes: ff1f7c17fb20 ("netdevsim: add pause frame stats")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

selftests: add a test for ethtool pause stats

Make sure the empty nest is reported even without stats.
Make sure reporting only selected stats works fine.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>