Enable external call support in AOSP dialer manifest.

            <meta-data android:name="android.telecom.IN_CALL_SERVICE_UI" android:value="true" />

            <meta-data android:name="android.telecom.IN_CALL_SERVICE_RINGING"

                android:value="false"/>

            <meta-data android:name="android.telecom.INCLUDE_EXTERNAL_CALLS"

                       android:value="true"/>

            <intent-filter>

                <action android:name="android.telecom.InCallService"/>

            </intent-filter>