[lib.index_set] Fix a bug in `add' where assert is performed
too early (e.g. before the assertion is actually required to
pass).
[snabbnfv-traffic] Extracted configuration logic to lib.nfv.config.
[bench/nfvconfig] Added nfvconfig benchmark design.
[bench/nfvconfig] Added fixtures for use with `bench/nfvconfig'
design.