logging: Improve instance logging filtering

Instance logging allows to set independent severity level for
each instance (static and runtime). However, so far when runtime
filtering was disabled, static level was not taken into account
and instance messages were only compile time filtered based on
module level.

Improved logging macros to use static instance level to determine
if message shall be created. It enables instance filtering also
when runtime filtering is disabled.

Signed-off-by: Krzysztof Chruscinski <krzysztof.chruscinski@nordicsemi.no>