simple_switch: use packet library

Also remove obsolete comments.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
of10: Register TCP_DST and UDP_DST headers in NXM

Signed-off-by: Can Zhang <can@canx.me>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>