Support for manual method + rearrange some code

Support for manual method + rearrange some code

Ticket: CM-1438
Reviewed By:
Testing Done:

- Moved link config to base ifupdown. I had been debating about this,
  this is need to support manual and also the --no-scripts option.
- helps executing only link up/down operations if needed on an interface
- While at it, i also moved the scheduler methods to be classmethods
  instead of instance methods (which again was a pending cleanup task)