Fix a crash in eng builds

CAPTIVE_PORTAL is a CS-managed capability, and causes CS to log a wtf.
When this test is run on an eng build, this sends SIGSEGV to the test,
which is pretty difficult to debug.

Test: FrameworksNetTests NetworkStackTests
Change-Id: I72fc46a6daa4e886425b4dc967318cca9f1a5302