Calculate priority based on caller configurations

Update NetworkPriorityClassifier to calculate priority
according to the VcnUnderlyingNetworkPriority list
configured in VcnGatewayConnectionConfig

Bug: 206044122
Test: atest FrameworksVcnTests(new)
Test: atest CtsVcnTestCses
Change-Id: I55afa916af44db655a568aae2488877f2c177d59