Notify call forwarding indicator when carrier configChanged is changed.

1.Fix a side-effect of aosp/1285363.
2.Move notifyCallForwardingIndicator from onSubscriptionsChanged() to onCarrierConfigChanged().

Bug: 181747913
Test: manual - verified whether CFU icon was appeared after reboot
Change-Id: I6ab9966231211008de604bdc6e07fad3e5ca24ef