Changed IncomingMessage for IncomingAccountMessage to solve
naming overlapping with one defined in CallManager signal API.

The old name is has been introduced into 2.2.x branch,
this new API will be also.

Refs #72396

Change-Id: I98bd6f1efa7b1c1671d963e353b105131249339f
(cherry picked from commit 5fa08a2e)