Received untagged traffic is treated as tagged with vlan 1 in case of existing sub-interfaces on this particular port.

[MaxYaremchuk]

Description

Received untagged traffic is treated as tagged with vlan 1 in case of existing sub-interfaces on this particular port.

Steps to reproduce the issue

1. Create two sub-interfaces Ethernet44.10, Ethernet44.20 and assign IP addresses on each of them and Ethernet44 as well:
   config interface ip add Ethernet44.10 100.10.0.1/24
config interface ip add Ethernet44.20 100.20.0.1/24
config interface ip add Ethernet44 100.0.0.1/24
2. Run untagged IP traffic from host "A" destined to 100.0.0.1 (Ethernet44)

Describe the results you received
This flow packets are treated as tagged with vlan1:

19:37:58.709257 00:11:01:00:00:03 > 24:8a:07:7e:4f:80, ethertype 802.1Q (0x8100), length 300: vlan 1, p 0, ethertype IPv4, (tos 0x0, ttl 64, id 0, offset 0, flags [none], proto unknown (61), length 282)
    100.0.0.2 > 100.0.0.1:  ip-proto-61 262

Although, from host "A" this flow’s packet was sourced untagged:

P.S. tagged with vlan 10 or 20 traffic destined to 100.10.0.1 and 100.20.0.1 respectively are processed successfully as expected.

Describe the results you expected
Received untagged traffic should be treated as untagged one.

Output of show version

SONiC Software Version: SONiC.HEAD.129-0c9040de
Distribution: Debian 9.11
Kernel: 4.9.0-9-2-amd64
Build commit: 0c9040de
Build date: Thu Nov 21 12:50:41 UTC 2019
Built by: johnar@jenkins-worker-4

Platform: x86_64-mlnx_msn2100-r0
HwSKU: ACS-MSN2100
ASIC: mellanox
Serial Number: MT1646X05314
Uptime: 19:48:39 up 18 min,  2 users,  load average: 3.10, 3.16, 2.40

Docker images:
REPOSITORY                 TAG                 IMAGE ID            SIZE
docker-syncd-mlnx          HEAD.129-0c9040de   4f3b126274c2        373MB
docker-syncd-mlnx          latest              4f3b126274c2        373MB
docker-fpm-frr             HEAD.129-0c9040de   7345e105bf26        321MB
docker-fpm-frr             latest              7345e105bf26        321MB
docker-sflow               HEAD.129-0c9040de   f240b81ea842        305MB
docker-sflow               latest              f240b81ea842        305MB
docker-lldp-sv2            HEAD.129-0c9040de   f1b94915bf13        299MB
docker-lldp-sv2            latest              f1b94915bf13        299MB
docker-dhcp-relay          HEAD.129-0c9040de   7ba3cee353b6        289MB
docker-dhcp-relay          latest              7ba3cee353b6        289MB
docker-database            HEAD.129-0c9040de   c5c92210277c        281MB
docker-database            latest              c5c92210277c        281MB
docker-snmp-sv2            HEAD.129-0c9040de   ad01f8a547b1        335MB
docker-snmp-sv2            latest              ad01f8a547b1        335MB
docker-orchagent           HEAD.129-0c9040de   7fc54899dc92        322MB
docker-orchagent           latest              7fc54899dc92        322MB
docker-teamd               HEAD.129-0c9040de   c0316e26bbbd        304MB
docker-teamd               latest              c0316e26bbbd        304MB
docker-sonic-telemetry     HEAD.129-0c9040de   43df42f49e91        304MB
docker-sonic-telemetry     latest              43df42f49e91        304MB
docker-router-advertiser   HEAD.129-0c9040de   b0aff9280842        281MB
docker-router-advertiser   latest              b0aff9280842        281MB
docker-platform-monitor    HEAD.129-0c9040de   10013f82e4d7        565MB
docker-platform-monitor    latest              10013f82e4d7        565MB

[liat-grozovik]

Issue will be handled by @deran1980