IpSecTransformState is a new API that exposed from a mainline module.
Ideally before SDK finalization, platform should check the API flag
com.android.net.flags.ipsec_transform_state before calling the API.
However the flag is defined in mainline module is not accessible from
the platform. Thus previously a placeholder flag was used.

This patch removes the usage of the placeholder flag. Instead the
code will check the availability of the API with a try catch block

Bug: 328844044
Test: atest FrameworksVcnTests && atest CtsVcnTestCases
Flag: NONE mainline API flag not accessible; using try catch
      block to gate the behavior
Change-Id: Ibbcb14817a6d714cdc99cf0894f1fc935a602a2c