Following the guideline of interfaces not allowed to declare anything
and not use prefix parameters, declare interfaces doing so as templates.
Also declare templates not using those features and not calling
templates themselves as interfaces.
These changes originate from the discussion in
https://github.com/TresysTechnology/selint/issues/205 and are found by
new proposed SELint checks at
https://github.com/TresysTechnology/selint/pull/206.
Signed-off-by: Christian Göttsche <cgzones@googlemail.com>