Use IkeProtocolException#getErrorType() to identify a specific error

AuthenticationFailedException and TemporaryFailureException
will not be System APIs. This patch changes VCN to use
IkeProtocolException#getErrorType to identify a specific
protocol error.

Test: atest FrameworksVcnTests
Bug: 175091931
Change-Id: Iaf3c1c9bd34957b0efdbfd7595c2838b56449308