bpf: reuse dev_is_mac_header_xmit for redirect

Commit dcf80034

 ("net/sched: act_mirred: Refactor detection whether
dev needs xmit at mac header") added dev_is_mac_header_xmit(); since it's
also useful elsewhere, move it to if_arp.h and reuse it for BPF.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>