Add psa_switch support

[WqyJh]

Fix #83

[onf-cla-manager[bot]]

Hi @WqyJh, this is the ONF bot 🤖 I'm glad you want to contribute to our projects! However, before accepting your contribution, we need to ask you to sign a Contributor License Agreement (CLA). You can do it online, it will take only a few minutes:

✒️ 👉 https://cla.opennetworking.org

After signing, make sure to add your Github user ID WqyJh to the agreement.

For more information or help:" https://wiki.opennetworking.org/x/BgCUI

[WqyJh]

Some how I failed to build the docker image. I tested by building the following Dockerfile as p4lang/p4app:latest.

FROM p4lang/p4app:latest

RUN rm -rf /scripts
COPY docker/scripts /scripts

It seems this repo isn't under actively maintainace, I'd like to take part in as a contributor.

[WqyJh]

See simple_switch_psa.p4app to run a psa test.