Issue 128554727: no merge option when press merge and swap buttons simultaneously.

[root cause  ]conferenceable of active call is null
[changes     ]ImsConferenceController recalculateConferenceable when add active connection

Change-Id: I63eb06295169dd328af0fd76743583bda4c77445
diff --git a/src/com/android/services/telephony/ImsConferenceController.java b/src/com/android/services/telephony/ImsConferenceController.java
index b193c7f..9932fab 100644
--- a/src/com/android/services/telephony/ImsConferenceController.java
+++ b/src/com/android/services/telephony/ImsConferenceController.java
@@ -154,6 +154,7 @@
         connection.addConnectionListener(mConnectionListener);
         connection.addTelephonyConnectionListener(mTelephonyConnectionListener);
         recalculateConference();
+        recalculateConferenceable();
     }
 
     /**