IMS: Merge calls option not seen when refer failed

calculating the conferenceable connections is not happening
when two calls are merged and the conference is formed with
only one participant and the call with second participant is
on hold.

Ensure conferenceable connections are calculated properly.
Fixes: 38365427
Test: Manual

Change-Id: I821a5478e5a90d1ab1c2a3ab1398eee169483278
1 file changed