Fixed incorrect merge service state

The existing logic for merging service state when device is on
IWLAN does not work properly on AP-assisted mode devices. Fixed
by copying the IWLAN preferred flag into IMS service state so
it can get the correct data RAT for AP-assisted mode devices.

Bug: 134706530
Test: WFC manual tests
Change-Id: Ic18934adb870a0114c913855cdb68e0ef33caa79

telephony/java/android/telephony/ServiceState.java

@@ -2035,4 +2035,18 @@ public class ServiceState implements Parcelable {
     public void setIwlanPreferred(boolean isIwlanPreferred) {
         mIsIwlanPreferred = isIwlanPreferred;
     }
+
+    /**
+     * @return {@code true} if any data network is preferred on IWLAN.
+     *
+     * Note only when this value is true, {@link #getDataNetworkType()} will return
+     * {@link TelephonyManager#NETWORK_TYPE_IWLAN} when AP-assisted mode device camps on both
+     * cellular and IWLAN. This value does not affect legacy mode devices as the data network
+     * type is directly reported by the modem.
+     *
+     * @hide
+     */
+    public boolean isIwlanPreferred() {
+        return mIsIwlanPreferred;
+    }
 }