I don't think anything needs to be changed. A javelin or any laser guided weapon requires 2 people to be involved (unlike the rape train that is a plane). In a vehicle, one person has to substitute a weapon for a designator and the guy doing the killing needs to equip that laser guided weapon.
One without the other is useless, so that javelin guy without designation can't do squat and the tank guy with guided missiles, without a designator, is pointless.
If people want to fight against laser designated items, they need to take reactive armour, stealth, IR smoke.
Another point is, if Javelins were not the only infantry items that could take down a plane then no so many would use them. Basically heli pilots are used to racking up 20 kill streaks and want to continue and don't like it that they can be shot down.