**- Why I did it**
Align style with slightly modified PEP8 standards (extend maximum line length to 120 chars). This will also help in the transition to Python 3, where it is more strict about whitespace, plus it helps unify style among the SONiC codebase. Will tackle other directories in separate PRs.
**- How I did it**
Using `autopep8 --in-place --max-line-length 120` and some manual tweaks.
* Fix some spelling error and add addition check in port_index_mapper.py script.
* Remove unneeded pyroute2 python module from sFlow container
Signed-off-by: Garrick He <garrick_he@dell.com>
**- Why I did it**
A memory issue was discovered during system test for scaling. The issue is documented here: https://docs.pyroute2.org/ipdb.html
> One of the major issues with IPDB is its memory footprint. It proved not to be suitable for environments with thousands of routes or neighbours. Being a design issue, it could not be fixed, so a new module was started, NDB, that aims to replace IPDB. IPDB is still more feature rich, but NDB is already more fast and stable.
**- How I did it**
- Rewrote the port_index_mapper.py script to use dB events.
- Convert to Python 3
