runtime: Make all methods in NetworkNotificationHandler pure virtual
runtime: Make all methods in NetworkNotificationHandler pure virtual

Sometimes failed with obscure 'missing sybols for vtable'

microflo/microflo,bergie/microflo,bergie/microflo,uwekamper/microflo-spiexperiment,rraallvv/microflo,rraallvv/microflo,uwekamper/microflo-spiexperiment,rraallvv/microflo,microflo/microflo,microflo/microflo,bergie/microflo,microflo/microflo,microflo/microflo,uwekamper/microflo-spiexperiment,rraallvv/microflo,microflo/microflo,bergie/microflo,uwekamper/microflo-spiexperiment