networkBandwidthGenericChecks: Drop useless check

networkBandwidthGenericChecks: Drop useless check

There's a check right at the beginning of the function that
shortcuts if the function was called over all NULL arguments.
However, this was meant just as a fool-proof check so that we
don't crash if function is used in a bad manner. Anyway, it makes
Coverity unhappy as it then thinks any of the arguments could be
NULL. Well, with the current state of the code it can't.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>