[Cleanup] Import naming should be consistent throughout the project

[Sam Betts]

There are several places in the code where we import the same thing but use different aliases.

For example in some places this is imported like:

    from neutron_lib import constants as l3_constants

and in other places:

    from neutron_lib import constants as n_constants

We should pick a style and keep in consistent throughout the networking-cisco code so that when switching between files you always know what your looking at.