[BOT.8] Dump BPF offload information in dumpsys

$ adb shell dumpsys tethering
BPF offload:
  Polling started
  Stats provider registered
  Upstream quota: {rmnet_data2=9223372036854775807}
  Forwarding stats:
    12(rmnet_data2) - ForwardedStats(rxb: 1065, rxp: 5, txb: 0, txp: 0)
  Forwarding rules:
    [wlan1]: iif(iface) oif(iface) v6addr srcmac dstmac
      12(rmnet_data2) 31(wlan1) /2401:e180:8831:77ae:a900:a03b:41fb..

Bug: 150736748
Test: Enable tethering on mobile data and check dumpsys tethering
Change-Id: I95ea3050d92f3ba8136a63cd399d3450d183c8dc