[docker-orchagent][201911] Pass ASIC vendor information to swss docker as docker level environment variable (#8274)

#### Why I did it
Recently, the reserved buffer of admin-down ports is going to be reclaimed.
However, the way to do this differs among vendors.
We need to find a way to pass vendor information to swss docker.

#### How I did it
Fetch the ASIC vendor information when the docker is created and pass it to the docker as environment variable `ASIC_VENDOR`.

files/build_templates/docker_image_ctl.j2

@@ -335,6 +335,9 @@ start() {
         -v /var/run/docker-syncd$DEV:/var/run/sswsyncd \
 {%- endif %}
 {%- endif %}
+{%- if docker_container_name == "swss" %}
+        -e ASIC_VENDOR={{ sonic_asic_platform }} \
+{%- endif %}
 {%- if docker_container_name == "bgp" %}
         -v /etc/sonic/frr/$DEV:/etc/frr:rw \
 {%- endif %}