Move BPF offload program from netd to mainline

Test: as the follows.
$ adb shell ls sys/fs/bpf | grep offload
map_offload_tether_ingress_map
map_offload_tether_limit_map
map_offload_tether_stats_map
prog_offload_schedcls_ingress_tether_ether
prog_offload_schedcls_ingress_tether_rawip

$ adb shell dumpsys netd --short
  TetherController
    BPF ingress map: iif(iface) v6addr -> oif(iface) srcmac ..
      13(rmnet_data3) 2401:e180:8842:6e3:bc6a:2e45:c30:f418 -> ..
    BPF stats (downlink): iif(iface) -> packets bytes errors
      13(rmnet_data3) -> 7 488 0
    BPF limit: iif(iface) -> bytes
      13(rmnet_data3) -> 9223372036854775807

Log:
bpfloader: Loaded object: /apex/com.android.tethering/etc/bpf/offload.o

Change-Id: I71b7efb1f4bd6eb1cd469a0e1e4a56342dc6e579