Skip some VCN unit tests on user builds

Configuring restricted transport types is for experiments purposes and
only allowed on a debuggable build. This patch ensures relevant unit
tests are skipped on user builds.

Since the experimental configurability is no longer needed anymore, there will be followup CLs to remove the feature and the tests.

Bug: 397874808
Test: run mts-user -m FrameworksVcnTests on a BP2A.250218.001 user build
Flag: EXEMPT; test code change
Change-Id: I9ca23b2901d740d3ddc5ba4febba4a300e0812bb