Not happening. Ethiopia is too mountainous and Portuguese resources are not enough to subdue Ethiopia in the 16th to 19th century.
That is the problem. A few hundred musketeers would do well against Somali's who are not using the same weapons. But when the Adal Sultanate gets help from the Ottomans with a few hundred/thousand soldiers and weapons it does not go well.
At best you get an alliance between Portugal and Ethiopia until Portugal loses posts in the Indian Ocean.
As previously mentioned, the idea here is to create some sort of agreement or allianceathat puts Portugal in a position of influence over Ethiopia, and eventually allows them to claim some sort of protectorate in a future ATL scramble for territories in Africa.
I believe that, if such a cooperation between the Ethiopians and the Portuguese is reached, you wouldn't see only a few hundred musketeers sent from Lisbon. Rather, after a while, the Ethiopians themselves could be using weapons supplied or bought from Portuguese ships in trade enclaves. Also, I think you may be overestimating not only actual Ottoman interest in the area, but also underestimating the capacity of this ATL Ethiopia to resist this interference, due to a number of factors.
Also, why is it "when" Portugal loses posts in the Indic Ocean? Are we really about to ignore butterflies here? The POD we're talking about here is about 70 years before King Sebastian's crusade, the iberian union and the Dutch revolt. It would be like saying that, based on a POD in the end of the HYW, most of England would still become Anglican.