Fix for GATT not returning disconnect callback.

Before recent refactor GATT was using the L2CAP layer to start LE
connections. Since the refactor, GATT talks directly to added
connection_manager, just like L2CAP.
L2CAP does have it's own timer for direct connections, that was
returning conneciton failure after timeout. After switching to
connection_manager, GATT no longer receives those callbacks.

This patch makes the connection_manager send the on_connection_timed_out
callback, and wire it to same handler that L2CAP layer was using before.

Test: unit tests added
Bug: 125553095
Change-Id: Iaf8be46fe8eed49f78ddbc6a2f3516bc8279e91f