Tests: Bluetooth: Host: Add ext-adv test to iterate reconnections

Where advertisement, connection and disconnection is iterated over 5
times, to verify the reestablishment of extended advertisements when
iterating over multiple times. Additionally, the connection
unreferencing has been decoupled from the disconnect event on both
sides, to demonstrate the dependency of the recycle event.

Signed-off-by: Luis Ubieda <luisf@croxel.com>