net: bpf: Allow TC programs to call BPF_FUNC_skb_change_head

This allows TC eBPF programs to modify and forward (redirect) packets
from interfaces without ethernet headers (for example cellular)
to interfaces with (for example ethernet/wifi).

The lack of this appears to simply be an oversight.

Tested:
  in active use in Android R on 4.14+ devices for ipv6
  cellular to wifi tethering offload.

Signed-off-by: Lorenzo Colitti <lorenzo@google.com>
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>