V2 requests are mistakenly being interpreted as v1 requests in params

[spacebear21]

Follow-up from #277 (review)

V2 requests are being sent with v=1 default send parameter and thus defaulting to disable_output_substitution = false. v1 requests over v2 directories are in the unsecured payment server category of BIP 78, so any v1 request has output substitution disabled. V2 requests are mistakenly being interpreted as v1 requests wrt Params.