Change the icon for the captive portal login app.

Looks like https://screenshot.googleplex.com/6n4Cf3LRv4A
Icon comes from frameworks/base/core/res/res/drawable/stat_notify_wifi_in_range.xml

Test: manual
Bug: 29924821
Change-Id: I378fdb2d493fb8598c3e4fa98e100696c72f88ea
Merged-In: I378fdb2d493fb8598c3e4fa98e100696c72f88ea
(cherry picked from commit 0b4e0750)