We have hundreds names all over Europe ending to *en.The most common original descriptive meaning for kalla in Finnish is a rocky island. Take a look at the kansalaisen karttapaikka. It is likely moved to new settlements from the seaside. Kalla-names are very old on the seaside, older than the eastern settlements. It can have another meaning in Livonia.
Getting back to the original sidestep, most probable explanation of the name Ikskile is a bridge or an other type of crossing located on an island of Daugava and managed by a Livonian family called Ikäinen/Ikeinen/Ikoinen, hence ?*Ikoisenkalla.