[202012][Buffer] Added cable length config to buffer config template for EdgeZoneAggregator

[developfast]

Why I did it

SONiC currently does not identify 'EdgeZoneAggregator' neighbor. As a result, the buffer profile attached to those interfaces uses the default cable length which could cause ingress packet drops due to insufficient headroom. Hence, there is a need to update the buffer templates to identify such neighbors and assign the same cable length as used by the T1.

Original PR for master: #14280

How I did it

Modified the buffer template to identify EdgeZoneAggregator as a neighbor device type and assign it the same cable length as a T1/leaf router.

How to verify it

Unit tests pass, and manually checked on a 7260 to see the changes take effect.

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

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

Description for the changelog

[Buffer] Added cable length config to buffer config template for EdgeZoneAggregator

Ensure to add label/tag for the feature raised. example - PR#2174 under sonic-utilities repo. where, Generic Config and Update feature has been labelled as GCU.

Link to config_db schema for YANG module changes

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

[developfast]

@qiluo-msft is it possible to quickly approve and merge this PR? #14280 is the master branch PR which has already been merged