Only call -rerouted callback if displayId changed

This moves the new listener callback method inside
the displayId conditional. Without this, the callback
is invoked for the initial Bubble activity start by
SystemUI.

Test: atest ActivityManagerMultiDisplayTests#testSingleTaskInstanceDisplay
Bug: 127322070
Change-Id: Ie8d0f4cef82ce77c2b806e9349ec60bc296ef726