[docker-lldp]: sonic advertise meaningful SysDescription instead of debian (sonic-net#6114)

Sonic devices advertise meaningful system description along with Debian package information.

before the fix:

-------------
admin@sonic:~$ show lldp neighbors
-------------------------------------------------------------------------------
LLDP neighbors:
-------------------------------------------------------------------------------
Interface: Ethernet0, via: LLDP, RID: 3, Time: 0 day, 16:36:30
SysName: sonic
SysDescr: Debian GNU/Linux 9 (stretch) Linux 4.9.0-11-2-amd64 #1 SMP Debian 4.9.189-3+deb9u2 (2019-11-11) x86_64
-------------------------------------------------------------------------------

After the fix:

root@sonic:~# show lldp neighbors Ethernet16
-------------------------------------------------------------------------------
LLDP neighbors:
-------------------------------------------------------------------------------
Interface:    Ethernet16, via: LLDP, RID: 10, Time: 0 day, 00:01:00
    SysName:      sonic
    SysDescr:     SONiC Software Version: SONiC.sonic_upstream_1.0_daily_201130_1501_62-dirty-20201130.203529 - HwSku: Accton-AS7816-64X - Distribution: Debian 10.6 - Kernel: 4.19.0-9-2-amd64
-------------------------------------------------------------------------------

Signed-off-by: sudhanshukumar22 <sudhanshu.kumar@broadcom.com>

Author: sudhanshukumar22

dockers/docker-lldp/Dockerfile.j2

@@ -43,6 +43,7 @@ COPY ["start.sh", "/usr/bin/"]
 COPY ["waitfor_lldp_ready.sh", "/usr/bin/"]
 COPY ["supervisord.conf.j2", "/usr/share/sonic/templates/"]
 COPY ["lldpd.conf.j2", "/usr/share/sonic/templates/"]
+COPY ["lldpdSysDescr.conf.j2", "/usr/share/sonic/templates/"]
 COPY ["lldpd", "/etc/default/"]
 COPY ["lldpmgrd", "/usr/bin/"]
 COPY ["files/supervisor-proc-exit-listener", "/usr/bin"]

dockers/docker-lldp/lldpdSysDescr.conf.j2

@@ -0,0 +1 @@
+configure system description "SONiC Software Version: SONiC.{{ build_version }} - HwSku: {{ DEVICE_METADATA['localhost']['hwsku'] }} - Distribution: Debian {{ debian_version }} - Kernel: {{ kernel_version }}"

dockers/docker-lldp/start.sh

@@ -1,4 +1,10 @@
 #!/usr/bin/env bash
+CFGGEN_PARAMS=" \
+    -d \
+    -t /usr/share/sonic/templates/lldpd.conf.j2 \
+    -y /etc/sonic/sonic_version.yml \
+    -t /usr/share/sonic/templates/lldpdSysDescr.conf.j2 \
+"
 
 if [ "${RUNTIME_OWNER}" == "" ]; then
     RUNTIME_OWNER="kube"
@@ -10,7 +16,7 @@ then
     ${CTR_SCRIPT} -f lldp -o ${RUNTIME_OWNER} -v ${IMAGE_VERSION}
 fi
 
-sonic-cfggen -d -t /usr/share/sonic/templates/lldpd.conf.j2 > /etc/lldpd.conf
+sonic-cfggen $CFGGEN_PARAMS > /etc/lldpd.conf
 
 mkdir -p /var/sonic
 echo "# Config files managed by sonic-config-engine" > /var/sonic/config_status