This type of crap from the Iranians is just regular business. They charge at a ship, are warned off, the US Navy fires a couple of warning shots across their bow and the Iranians go home. Normally, if the Iranians didn't turn back and they got within 1000 feet of the ship, they would be turned into falafel by 30mm auto-cannon, and the Iranians know it. Which is exactly why they turn away at the first warning shot.
The conventional rules of the sea, so to speak, if you are approaching a ship of any kind on anything resembling and intercept course, you should hail that vessel and likewise, the vessel being intercepted should do likewise. If a vessel approaches you on an intercept course and does not respond to a hail, it is considered an act of hostility to which a violent response is the norm.
Personally, I would find a way to humiliate this Iranian 'Attack Boats', something like intercepting the attack boat with a helicopter and dump several thousand gallons of human excrement from the bilge tanks on them.