This is a detail from a picture of the Konigsberg gun captured at Bagamoyo. The photo was apparently taken by a British sailor from HMS
Vengeance, which was involved in the attack.
If as seems likely the photo was taken not long after the attack (though I don't know how long HMS
Vengeance stuck around after) then it's hard to see who this chap guarding the gun could be other than an Askari of the Zanzibar Rifles (the KAR were not to my knowledge involved in the attack). He seems to be armed with a Martini-Enfield with rather a long pig-sticker attached. I think by 1916 the KAR all had Lee-Enfields, but I'm not positive on that. Interestingly in late 1916, the Zanzibar Rifles were merged with the Mafia Armed Constabulary to form 7 KAR.
Could be what you're looking for, but I don't have an ironclad identification as to who this chap is. Best I've got, I'm afraid.