[SNMP] Fix config template issue when setting snmpagentaddress (#20152)

Related to PR#16187

Why I did it
When you configure an SNMP agent address with a VRF, the snmpd service will fail to properly start after the configuration has been applied. The snmpd service shows a status of "FATAL."

sudo config snmpagentaddress add 1.1.1.1 -p 161 -v mgmt

docker exec -it snmp supervisorctl status | awk '{print $1, $2}'
dependent-startup RUNNING
rsyslogd RUNNING
snmp-subagent STOPPED
snmpd FATAL
start EXITED
supervisor-proc-exit-listener RUNNING
Work item tracking
Microsoft ADO (number only):
How I did it
Corrected syntax in the jinja template used to generate the snmpd.conf within the SNMP docker container.

How to verify it
sudo config snmpagentaddress add 1.1.1.1 -p 161 -v mgmt

docker exec -it snmp supervisorctl status | awk '{print $1, $2}'
dependent-startup EXITED
rsyslogd RUNNING
snmp-subagent RUNNING
snmpd RUNNING
start EXITED
supervisor-proc-exit-listener RUNNING

Author: brholmes1

dockers/docker-snmp/snmpd.conf.j2

@@ -26,7 +26,7 @@
 
 {% if SNMP_AGENT_ADDRESS_CONFIG %}
 {% for (agentip, port, vrf) in SNMP_AGENT_ADDRESS_CONFIG %}
-agentAddress {{ protocol(agentip) }}:[{{ agentip }}]{% if port %}:{{ port }}{% endif %}{% if vrf %}%{{ vrf }}{% endif %}{{ "" }}
+agentAddress {{ protocol(agentip) }}:[{{ agentip }}]{% if vrf %}@{{ vrf }}{% endif %}{% if port %}:{{ port }}{% endif %}{{ "" }}
 {% endfor %}
 {% else %}
 agentAddress udp:161