Fix negative uid stats caused by 464xlat adjust when eBPF is on.

When using xt_qtaguid to count per uid stats,
NetworkStatsService needs to adjust the 464xlat traffic since
iptables module would double count for ipv4 and ipv6 packet.
But for eBPF, the per uid stats is collected in a different
hook, so the adjustment on root uid would only be needed in tx
direction.

Bug: 112226716
Test: 1. Make ipv4 traffic in ipv6-only network and check data
         usage.
      2. Make ipv4 traffic in a client which connect to
         ipv6-only hotspot.
      3. runtest frameworks-net
      4. cts-tradefed run cts -m CtsNetTestCases -t \
                 android.net.cts.TrafficStatsTest
      5. cts-tradefed run cts -m CtsUsageStatsTestCases

Change-Id: Ic9a84f5446eddc943c255d5f3b89dad171f53cac