Add tests for DhcpErrorEvent

The tests are run both in unit and CTS tests.
Test: atest FrameworksNetTests NetworkStackTestCases
Bug: 129200175

Change-Id: I78d78dd421cc3ffea774ff5eaa6aa758debc9cf2
Merged-In: I9b65a2eef94567d2b79a9955619938e64906080d
Merged-In: I78d78dd421cc3ffea774ff5eaa6aa758debc9cf2
(cherry picked from commit 9e046d509a37c6f37b4757f1681846cee60cfd5c)
6 files changed