bpf_progs/clatd - do not tx offload ipv4/udp packets with 0 checksum

Test: builds, treehugger
Bug: 160191447
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Original-Change: https://android-review.googlesource.com/1363156
Merged-In: I483f65c16e55dc5851e0bea9b45e8fdfa283d9a9
Change-Id: I483f65c16e55dc5851e0bea9b45e8fdfa283d9a9