xdp: Add tracepoint for bulk XDP_TX

This is introduced for admins to check what is happening on XDP_TX when
bulk XDP_TX is in use, which will be first introduced in veth in next
commit.

v3:
- Add act field to be in line with other XDP tracepoints.

Signed-off-by: Toshiaki Makita <toshiaki.makita1@gmail.com>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>