Not a violation of net neutrality
Net neutrality is about passing others' data neutrally as a carrier. Netflix is restricting their own data as a content provider. Not the same thing at all.
The way I see it, Netflix is trying to help their customers by keeping costs down. Their mistake was not being transparent about it, and not giving customers the choice to decide for themselves. Unwise, yes, but I see no evil intent, at least not with regards to the throttling itself.
"Netflix said it doesn’t limit its video quality at two carriers: T-Mobile and Sprint Corp., because “historically those two companies have had more consumer-friendly policies.” When customers exceed their data plans on Sprint or T-Mobile, the carriers usually slow their network connections, rather than charge overage fees." I pulled that quote from Techdirt, but I believe they were quoting from WSJ.
It looks like they're now going to offer the ability to make the choice yourself, so that's that part sorted. If you want to boycott them for being dishonest by omission, go for it, but I don't see this as hypocrisy myself.
https://www.techdirt.com/articles/20160325/05264934013/netflix-reveals-it-throttles-att-verizon-customers-to-save-them-usage-caps-overage-fees.shtml