ifPhysAddress MIB doesn't return Mac address

[AndriiLozovyi]

Description
SNMP walk for OID 1.3.6.1.2.1.2.2.1.6 return empty strings instead of physical address of ports.

Steps to reproduce the issue:

1. Bring up t0 or t1 topology
2. Trigger SNMP walk : snmpwalk -v 2c -c public 1.3.6.1.2.1.2.2.1.6

Describe the results you received:

iso.3.6.1.2.1.2.2.1.6.1 = ""
iso.3.6.1.2.1.2.2.1.6.5 = ""
iso.3.6.1.2.1.2.2.1.6.9 = ""
iso.3.6.1.2.1.2.2.1.6.13 = ""
iso.3.6.1.2.1.2.2.1.6.17 = ""
iso.3.6.1.2.1.2.2.1.6.21 = ""
iso.3.6.1.2.1.2.2.1.6.25 = ""
iso.3.6.1.2.1.2.2.1.6.29 = ""
iso.3.6.1.2.1.2.2.1.6.33 = ""
iso.3.6.1.2.1.2.2.1.6.37 = ""
iso.3.6.1.2.1.2.2.1.6.41 = ""
iso.3.6.1.2.1.2.2.1.6.45 = ""
iso.3.6.1.2.1.2.2.1.6.49 = ""
iso.3.6.1.2.1.2.2.1.6.53 = ""
iso.3.6.1.2.1.2.2.1.6.57 = ""
iso.3.6.1.2.1.2.2.1.6.61 = ""
iso.3.6.1.2.1.2.2.1.6.65 = ""
iso.3.6.1.2.1.2.2.1.6.69 = ""
iso.3.6.1.2.1.2.2.1.6.73 = ""
iso.3.6.1.2.1.2.2.1.6.77 = ""
iso.3.6.1.2.1.2.2.1.6.81 = ""
iso.3.6.1.2.1.2.2.1.6.85 = ""
iso.3.6.1.2.1.2.2.1.6.89 = ""
iso.3.6.1.2.1.2.2.1.6.93 = ""
iso.3.6.1.2.1.2.2.1.6.97 = ""
iso.3.6.1.2.1.2.2.1.6.101 = ""
iso.3.6.1.2.1.2.2.1.6.105 = ""
iso.3.6.1.2.1.2.2.1.6.109 = ""
iso.3.6.1.2.1.2.2.1.6.113 = ""
iso.3.6.1.2.1.2.2.1.6.117 = ""
iso.3.6.1.2.1.2.2.1.6.121 = ""
iso.3.6.1.2.1.2.2.1.6.125 = ""
iso.3.6.1.2.1.2.2.1.6.129 = ""
iso.3.6.1.2.1.2.2.1.6.133 = ""
iso.3.6.1.2.1.2.2.1.6.137 = ""
iso.3.6.1.2.1.2.2.1.6.141 = ""
iso.3.6.1.2.1.2.2.1.6.145 = ""
iso.3.6.1.2.1.2.2.1.6.149 = ""
iso.3.6.1.2.1.2.2.1.6.153 = ""
iso.3.6.1.2.1.2.2.1.6.157 = ""
iso.3.6.1.2.1.2.2.1.6.161 = ""
iso.3.6.1.2.1.2.2.1.6.165 = ""
iso.3.6.1.2.1.2.2.1.6.169 = ""
iso.3.6.1.2.1.2.2.1.6.173 = ""
iso.3.6.1.2.1.2.2.1.6.177 = ""
iso.3.6.1.2.1.2.2.1.6.181 = ""
iso.3.6.1.2.1.2.2.1.6.185 = ""
iso.3.6.1.2.1.2.2.1.6.189 = ""
iso.3.6.1.2.1.2.2.1.6.193 = ""
iso.3.6.1.2.1.2.2.1.6.197 = ""
iso.3.6.1.2.1.2.2.1.6.201 = ""
iso.3.6.1.2.1.2.2.1.6.205 = ""
iso.3.6.1.2.1.2.2.1.6.209 = ""
iso.3.6.1.2.1.2.2.1.6.213 = ""
iso.3.6.1.2.1.2.2.1.6.217 = ""
iso.3.6.1.2.1.2.2.1.6.221 = ""
iso.3.6.1.2.1.2.2.1.6.225 = ""
iso.3.6.1.2.1.2.2.1.6.229 = ""
iso.3.6.1.2.1.2.2.1.6.233 = ""
iso.3.6.1.2.1.2.2.1.6.237 = ""
iso.3.6.1.2.1.2.2.1.6.241 = ""
iso.3.6.1.2.1.2.2.1.6.245 = ""
iso.3.6.1.2.1.2.2.1.6.249 = ""
iso.3.6.1.2.1.2.2.1.6.253 = ""
iso.3.6.1.2.1.2.2.1.6.1001 = ""
iso.3.6.1.2.1.2.2.1.6.1002 = ""
iso.3.6.1.2.1.2.2.1.6.1003 = ""
iso.3.6.1.2.1.2.2.1.6.1004 = ""
iso.3.6.1.2.1.2.2.1.6.10000 = ""

Describe the results you expected:
Expected to receive physical address of ports instead of empty strings.

Additional information you deem important (e.g. issue happens only occasionally):

**Output of `show version`:**

```
SONiC.master.134-dirty-20210225.114416
Distribution: Debian 10.8
Kernel: 4.19.0-12-2-amd64
Build commit: 2a339faf
Build date: Thu Feb 25 11:54:08 UTC 2021
Platform: x86_64-arista_7170_64c
HwSKU: Arista-7170-64C
```

**Attach debug file `sudo generate_dump`:**

```
(paste your output here)
```

[AndriiLozovyi]

@lguohan, @bingwang-ms Could you please take a look ?
Looks like it isn't implemented rfc1213