Enhance FGNHG CLI to filter by and show vnet + prefix

[NavdhaJindal]

What I did

CLI enhancement for fine grained ecmp routes, to show fg routes by specifying vnet and prefix.

New CLI added:

show fgnhg hash-view <vnet/vrf name> <prefix name>
show fgnhg active-hops <vnet/vrf name> <prefix name>

How I did it

Accept 2 positional args instead of 1. Depending on number of args, filter for:

• 1 arg: nhg
• 2 args: vnet and prefix

How to verify it

Usage:

$show fgnhg active-hops Vnet200 30.0.1.2/32
VNET/VRF    FG NHG Prefix    Active Next Hops
----------  ---------------  ------------------
Vnet200     30.0.1.2/32      10.10.10.20
                             10.10.2.1
                             10.10.2.2
                             10.10.2.3
                             10.10.2.4
                             10.10.2.5
                             10.10.2.6
                             10.10.2.7

$ show fgnhg active-hops
VNET/VRF    FG NHG Prefix    Active Next Hops
----------  ---------------  ------------------
default     100.1.1.0/24     10.0.0.57
	                             10.0.0.59
	                             10.0.0.61
	                             10.0.0.63
Vnet1       180.0.3.1/32     100.0.1.0
	                             100.0.1.1
                                     100.0.1.2                            

$show fgnhg hash-view Vnet200 30.0.1.2/32
VNET/VRF    FG NHG Prefix    Next Hop     Hash buckets
----------  ---------------  -----------  --------------
Vnet200     30.0.1.2/32      10.10.10.20  7   15
Vnet200     30.0.1.2/32      10.10.2.1    0   8
Vnet200     30.0.1.2/32      10.10.2.2    1   9
Vnet200     30.0.1.2/32      10.10.2.3    2   10
Vnet200     30.0.1.2/32      10.10.2.4    3   11
Vnet200     30.0.1.2/32      10.10.2.5    4   12
Vnet200     30.0.1.2/32      10.10.2.6    5   13
Vnet200     30.0.1.2/32      10.10.2.7    6   14

$ show fgnhg hash-view
VNET/VRF    FG NHG Prefix    Next Hop    Hash buckets
----------  ---------------  ----------  --------------------------
default     100.1.1.0/24     10.0.0.57   0   4   8   12  16
default     100.1.1.0/24     10.0.0.59   1   5   9   13  17
default     100.1.1.0/24     10.0.0.61   2   6   10  14  18
default     100.1.1.0/24     10.0.0.63   3   7   11  15  19
Vnet1       180.0.3.1/32     100.0.1.0   0   3   6   9   12  15  18
Vnet1       180.0.3.1/32     100.0.1.1   1   4   7   10  13  16  19
Vnet1       180.0.3.1/32     100.0.1.2   2   5   8   11  14  17

Previous command output (if the output of a command-line utility has changed)

New command output (if the output of a command-line utility has changed)

[mssonicbld]

/azp run

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[Copilot]

Pull request overview

Enhances the show fgnhg CLI to surface VRF/VNET context (by adding a VNET/VRF column) and introduces a new 2-argument filter mode intended to query FGNHG data by (vrf, prefix).

Changes:

• Added FG_ROUTE_TABLE key parsing and reused hash-bucket formatting logic to support VRF-aware output.
• Updated show fgnhg {hash-view,active-hops} output to include VNET/VRF and added (vrf, prefix) filtering via positional args.
• Extended unit-test mock STATE_DB data and updated/added pytest expectations for the new output and filter behavior.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 9 comments.

File	Description
show/fgnhg.py	Adds VRF-aware key parsing/formatting and new positional-argument filtering modes for hash-view and active-hops.
tests/fgnhg_test.py	Updates expected CLI output to include VNET/VRF and adds tests for (vrf, prefix) filtering and invalid VRF handling.
tests/mock_tables/state_db.json	Adds a VRF/VNET-scoped `FG_ROUTE_TABLE

[mssonicbld]

/azp run

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: NavdhaJindal / name: Navdha Jindal (33cecf3, 60780c0)

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[radha-danda]

@NavdhaJindal, Please fix PR checks

[mssonicbld]

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[prsunny]

Changes lgtm, Please fix PR checker failures

[mssonicbld]

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[mssonicbld]

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[mssonicbld]

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[mssonicbld]

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[prsunny]

@qiluo-msft , would you help with merge?