Use #setNetwork and #getNetwork for IkeSessionParams

This pacth changes VCN to call #setNetwork and #getNetwork instead
of #setConfiguredNetwork and #getConfiguredNetwork because the
later two methods will not be APIs.

This patch also changes VCN unit tests to build an IkeSessionParams
without a Context because the constructor requring a Context
is deprecated.

Bug: 180521384
Test: FrameworksVcnTests, CtsVcnTestCases
Change-Id: I971d0d1b6824890c58263a1960f3b8d0e66fe7d1