[pft_docker] Checks out the update of gNMI client script. (#11450)

Signed-off-by: Yong Zhao yozhao@microsoft.com

Why I did it
This PR aims to check in the commit f2b11e4 introduced by the update related to gNMI python client.

How I did it
I changed the Dockfile.j2 such that the update of gNMI client script will be checked in when ptf docker image is built.

How to verify it
A PTF container image was built and then loaded on a testbed. I checked the update of gNMI client script was checked in.

dockers/docker-ptf/Dockerfile.j2

@@ -206,7 +206,7 @@ RUN mkdir -p /var/log/supervisor
 # Install Python-based GNMI client
 RUN git clone https://github.com/lguohan/gnxi.git \
     && cd gnxi \
-    && git checkout 53901ab \
+    && git checkout f2b11e4 \
     && cd gnmi_cli_py \
     && pip install -r requirements.txt