Garaad diinle
I've actually considered this a while back but it's hard to argue that solate is the same thing as somali. At best it might've been the name of a clan if anything.“I subjugated the peoples of Rauso who live in the midst of incense-gathering Barbarians between great waterless plains, and I subjugated the people of Solate, whom I ordered to guard the coasts of the sea. All these people, enclosed by mighty mountains”
This could be an even older mention, it’s from an Adulite throne which dates back to the 3rd century.
As for the text itself it's clearly mentioning a part of northern somalia but the extend of it's claims cannot be ascertained. For one this is the only text to claim any kind of control over these lands and ezana who came less than a century later didn't include these lands as part of his domain.
The kings of axum were also known to claim land they had no control over for example again ezana who claimed to be king of thu raydan, himyar and saba all of whom were independent kingdoms. If anything the text could at most be talking about a simple raid especially since there is no mention of permeant settlement on the lands of frankincense.