Fix for GATT not returning disconnect callback.

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