Enable iWlan legacy mode

Bug: 143666962
Test: flash TH ROM and check
  (1) ro.telephony.iwlan_operation_mode is set to "legacy"
  (2) set persist.vendor.radio.adb_log_on to 1 and see
  below log in adb logcat log:
  11-01 15:57:29.926 14487 14487 F RILQ    :
  [Log.cpp: 48] [qcrild(14487,14487)] d: [DataModule]:
  IWLAN mode system property is legacy

Change-Id: I24c995cb1d1667d9042a58b74a26da60938aae6b