Provide more feedback to Settings when sessions fail

This change updates the VPN state when IKEv2 sessions fail, and when
configuration errors occur.

Bug: 162289824
Test: Manual testing with IKEv2/PSK
Change-Id: I2e8c6f421d2898f97b0ac422b2276edf9ef923f1
Merged-In: I2e8c6f421d2898f97b0ac422b2276edf9ef923f1
(cherry picked from commit 0be82d4f)