[action] [PR:17784] [dualtor] Disable zebra link-detect for vlan interfaces

[mssonicbld]

Why I did it

If all vlan member ports are admin down, the vlan route is removed by FRR, so the packets to the vlan subnet will be forwarded with the default route, two issues:

1. route inconsistency between kernel and ASIC.
   the vlan route in kernel still has nexthop as the vlan device, the vlan route in ASIC has nexthop as the default route.
2. no tunnel will be created.
   As those traffic will be bounced back to T1s by the ASIC, they will not be able to be trapped to kernel to trigger the zero-mac tunnel route creation.

For dualtor, the downstream standby traffic should be tunneled to the active side.
To ensure the zero-mac tunnel route works as expected, the vlan route should always present in both the kernel and ASIC.
So let's disable the link-detect for vlan interfaces.

Fixes: #16085

Signed-off-by: Longxiang Lyu [email protected]

Work item tracking

• Microsoft ADO (number only): 26325737

How I did it

Disable the link-detect flag in the frr zebra template.

How to verify it

UT and nightly run.

Which release branch to backport (provide reason below if selected)

• 201811
• 201911
• 202006
• 202012
• 202106
• 202111
• 202205
• 202211
• 202305

Tested branch (Please provide the tested image version)

Description for the changelog

Link to config_db schema for YANG module changes

A picture of a cute animal (not mandatory but encouraged)

[mssonicbld]

Original PR: #17784