The Protection reaction on the Warforged Soldier Statblock states:
Protection. When an attacker the warforged can see makes an attack roll against a creature within 5 feet of the warforged, the warforged can impose disadvantage on the attack roll.
So my thinking is as follows: The Warforged is within 5 feet of himself... thus if he is the target of an attack, he can use the reaction. I am not sure though if this is intended by the rules or if I'm thinking it right.
Would the Warforged Soldier be considered a creature within 5 feet of himself?
