help: Restart SNMP service

run:
      if cli-shell-api existsActive service snmp; then
          echo "Restarting SNMP..."
          sudo /opt/vyatta/sbin/vyatta-snmp.pl --restart-snmp;
          if [[ $? -eq 0 ]]; then
              echo "Success!"
          fi
      else
          echo "SNMP is not configured"
      fi