Fix: make sure no index is in flight before using inactivity beacons

Since the index is sent in two parts on two separate connections from
the consumer, there can be cases where we receive an inactivity beacon
between the index creation and the data reception.

This fix prevents from using the inactivity beacon if we know a data
index is coming.

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
Signed-off-by: David Goulet <dgoulet@efficios.com>