I'm going to give a bit of an ugly answer:
- You don't know what your primary function is
- Your beef isn't with the Sales Department.
Let me explain what I mean by that.
You mention that you keep getting pulled from your "primary function", and that your CEO and CTO are fine with this. Well... no. If the CEO and CTO are both saying they want you to spend most of your time working on XYZ... you can't call something else your "primary function". You may want it to be your primary function, but ultimately the CEO/CTO are setting your priorities. They get to decide what your primary functions are while you work for the company. Developing new features requested by sales is one of your primary functions.
Second, your Sales team isn't actually doing anything wrong, not exactly. If the CEO is okay with the Sales team deciding what the priorities are for future development, and the Sales team isn't promising anything undeliverable, and the CEO is approving of the Sales team actions? Then the Sales team isn't overstepping: they've been given the authority to decide what features should go into future releases. Getting mad or trying to change the behavior of anyone on the Sales team is pointless; within the current company dynamic, they're not actually doing anything wrong.
So, going forward?
First up, instead of focusing on the Sales team, build a case for why your team would be an asset for planning of future development - and try to convince the CEO/CTO that you need to be involved. Because, right now, they don't think you are - if they did, they wouldn't let the sales team decide future functionality without you.
Second, change your mental attitude on the process. Between the tenor of your question, your mentioning of frustration, and your comment asking if you should sabotage the sales team? You're spinning your wheels in a way that's neither helpful to yourself or to your company. Instead of focusing on "But this isn't what I want my priority to be!" - focus on what your sprint tasks are, and do them as good as you possibly can.
... actually, change the order on those. It'd be tough to convince people you'd be an asset to strategic planning while you're in the mindset that sabotaging the sales team is a good idea.