Set NOT_VCN_MANAGED capability for Networks in VcnMgmtSvc.

This CL updates VcnManagementService to set the NOT_VCN_MANAGED bit for
Networks that are not VCN-managed. This ensures that Networks correctly
regain the NOT_VCN_MANAGED bit after leaving a VCN.

Bug:
Test: atest FrameworksVcnTests CtsVcnTestCases
Change-Id: I01ffdde246e602296673675add58c47c92b15994