The unconscious condition states the following two effects (PHB 292):
The creature drops whatever it's holding and falls prone.
Attack rolls against the creature have advantage
Under the prone condition it says (ibid):
An attack roll against the creature has advantage if the attacker is within 5 feet of the creature. Otherwise, the attack roll has disadvantage.
The rules of advantage/disadvantage include the following paragraph (PHB 171):
If circumstances cause a roll to have both advantage and disadvantage, you are considered to have neither of them, and you roll one d20. This is true even if multiple circumstances impose disadvantage and only one grants advantage or vice versa. In such a situation, you have neither advantage nor disadvantage.
The question then is, does one receive advantage for a non-adjacent attack against an unconscious foe?
Are the effects of unconsciousness written to define the condition as it is, or are we meant to "calculate" the full truth by recognizing that the unconscious advantage and prone disadvantage (of non-adjacent attacks) should cancel out?