Add feature flag annotations to netpolicy cts The code was in a project that did not allow use of flag-junit. Now we can use the appropriate annotations to check flag value and skip the test if necessary. Flag: TEST_ONLY Test: atest CtsHostsideNetworkPolicyTests Bug: 321848487 (cherry picked from https://googleplex-android-review.googlesource.com/q/commit:1339d2f9dce6290383ec7da84a6a2aa2d09c5a0d) Merged-In: I798e283358b8f02f13556510d676725ef3b76cd6 Change-Id: I798e283358b8f02f13556510d676725ef3b76cd6