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
12 files changed