Adding host version of net_flags_lib

This is required to annotated hostside tests with appropriate flag
requirements

Flag: TEST_ONLY

Test: atest CtsHostsideNetworkPolicyTests

Bug: 321848487
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:26d58e1533414c766c5752e5d2a237017aeb6af9)
Merged-In: Ieabd7ea363dbae5a1d0f65fb74f484a04a845ea7
Change-Id: Ieabd7ea363dbae5a1d0f65fb74f484a04a845ea7