Do not pass EVENT_MERGE_START for ImsConference.

A change was made to pass other connection events from the host connection
to the ImsConference.  This means that the host conference will pass
EVENT_MERGE_START for conferences, which was not done in the past (it is
normally only sent for calls being merged INTO a conference, not on the
conference itself).

Test: Manually reproduce and verify that the merge start event is not
passed.
Bug: 133128377

Change-Id: Ib1d28909f3d78416b3cebd21848b033a8b88e261
diff --git a/src/com/android/services/telephony/ImsConference.java b/src/com/android/services/telephony/ImsConference.java
index 9b66487..9cb587c 100644
--- a/src/com/android/services/telephony/ImsConference.java
+++ b/src/com/android/services/telephony/ImsConference.java
@@ -212,6 +212,12 @@
 
         @Override
         public void onConnectionEvent(Connection c, String event, Bundle extras) {
+            if (Connection.EVENT_MERGE_START.equals(event)) {
+                // Do not pass a merge start event on the underlying host connection; we only
+                // indicate a merge has started on the connections which are merged into a
+                // conference.
+                return;
+            }
             sendConnectionEvent(event, extras);
         }
     };