Add methods for updating ingressDiscardRule bpf map to BpfNetMaps

Cherry-pick of aosp/2795710 to backport VPN security fix to non-mainline
U devices with minor conflicts resolution.
Since U branches use module prebuilt and new tests in
BpfNetMapsTest.java relies on InetAddressUtils change in this topic,
this CL does not add tests for setIngressDiscardRule and
removeIngressDiscardRule.

Bug: 193031925
Test: NetworkStaticLibsTests
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:b01647922d2b393fd705bf7fd68fbe10ccdffdc4)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:63e35f76ce93bc4d4ecfe7802f6fba84cb99d0f0)
Merged-In: Ie7057eb0273023767489ea72ea1faf9598724ef9
Change-Id: Ie7057eb0273023767489ea72ea1faf9598724ef9