The default action for unlisted tests is "not-supported", so given that
ipoib doesn't support ETH_SS_TEST, there is no need to check for it
in the case statements, just let it get caught by the default: case.

Fixes: e3614bc9 ("IB/ipoib: Add readout of statistics using ethtool")
Signed-off-by: Kamal Heib <kamalheib1@gmail.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>