pkg/nimble/netif: adapt ops->init to handle driver initialization
pkg/nimble/netif: adapt ops->init to handle driver initialization

RIOT-OS/RIOT,ant9000/RIOT,kaspar030/RIOT,kaspar030/RIOT,OlegHahm/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,jasonatran/RIOT,kYc0o/RIOT,kYc0o/RIOT,kaspar030/RIOT,jasonatran/RIOT,kYc0o/RIOT,kaspar030/RIOT,OlegHahm/RIOT,miri64/RIOT,RIOT-OS/RIOT,miri64/RIOT,kaspar030/RIOT,miri64/RIOT,jasonatran/RIOT,ant9000/RIOT,kYc0o/RIOT,ant9000/RIOT,ant9000/RIOT,RIOT-OS/RIOT,miri64/RIOT,jasonatran/RIOT,miri64/RIOT,OlegHahm/RIOT,ant9000/RIOT,kYc0o/RIOT,OlegHahm/RIOT