packet-netflow.c: Do various fixes and changes

- Allow integer & float fields to have "reduced size encoding";
   Fixes Bug #8846;
- Add a missing cflow field-type;
- Update the names of a few cflow field-types;
- Replace all-but-one use of proto_tree_add_text();
- Fix encoding-args as appropriate;
- Remove some obsolete comments;
- Adust whitespace/indentation/formatting.

Change-Id: I4271e3692288cef3ea0f1aa5eb44f5a0b05c29da
Reviewed-on: https://code.wireshark.org/review/4348
Petri-Dish: Bill Meier <wmeier@newsguy.com>
Reviewed-by: Bill Meier <wmeier@newsguy.com>