Correct propagation of asynchonous events

The legacy plugin listener was not set when used in
passthrough mode in Treble. This caused events (session renewal,
key expired etc) not to be propagated to the app.

b/35375500

Test: In progress

Change-Id: I7d74b3320c82e22f67d3c804ee93f9b9791080b2
(cherry picked from commit 89437fbd)