yang: Fix pyang errors in frr-bgp-types.yang

[y-bharath14]

Fix pyang errors in frr-bgp-types.yang

frr-bgp-types.yang:40: error: RFC 8407: 4.8: statement "revision" must have a "reference" substatement
frr-bgp-types.yang:45: error: RFC 8407: 4.13,4.14: statement "typedef" must have a "description" substatement
frr-bgp-types.yang:49: error: RFC 8407: 4.13,4.14: statement "typedef" must have a "description" substatement
frr-bgp-types.yang:53: error: RFC 8407: 4.13,4.14: statement "typedef" must have a "description" substatement
frr-bgp-types.yang:57: error: RFC 8407: 4.13,4.14: statement "typedef" must have a "description" substatement
frr-bgp-types.yang:77: error: RFC 8407: 4.13,4.14: statement "typedef" must have a "description" substatement
frr-bgp-types.yang:97: error: RFC 8407: 4.13,4.14: statement "typedef" must have a "description" substatement
frr-bgp-types.yang:117: error: RFC 8407: 4.13,4.14: statement "typedef" must have a "description" substatement
frr-bgp-types.yang:137: error: RFC 8407: 4.13,4.14: statement "typedef" must have a "description" substatement

[greptile-apps]

Greptile Overview

Greptile Summary

This PR fixes RFC 8407 compliance issues in yang/frr-bgp-types.yang by adding missing descriptions to all typedef statements and a reference to the revision statement. The changes address all 9 pyang errors listed in the PR description:

• Added reference "FRRouting" to the revision statement
• Added descriptions to 8 typedef statements: plist-ref, access-list-ref, as-path-filter-ref, bgp-instance-type, as-type, add-path-type, bfd-session-type, and direction

All descriptions are clear, concise, and accurately describe the purpose of each typedef. The changes are purely documentation-related and do not affect any functionality.

Confidence Score: 5/5

• This PR is safe to merge with no risk
• The changes are purely additive documentation improvements that add RFC 8407 compliance to the YANG model without modifying any functional code or data types
• No files require special attention

Important Files Changed

Filename	Overview
yang/frr-bgp-types.yang	Added RFC 8407 compliant descriptions to all typedefs and reference to revision statement