doc: Fix VRF-related and PIM docs

[gromit1811]

Update VRF-related and specifically PIM docs to improve readability, comprehensibility and correctness. For details, see the individual commit messages.

Some notes:

For reviewing, using git diff --word-diff is recommended. This will significantly reduce the diff size for cases where I just changed the capitalization of acronyms or reformatted due to overly long lines.

I tried to improve the readability by capitalizing acronyms. I've done this where I stumbled across it, can't promise full coverage.

The last commit 9310485 updates the documentation regarding VRF-awareness of PIM parameters in the current FRR Git master. There are discussions ongoing in the pimd channel in Slack to make all 3 parameters VRF-aware. If that results in an implementation before this PR gets merged, I'll drop that commit. Otherwise, I'd suggest to merge it now and revert it when the implementation is finished.

[greptile-apps]

Greptile Overview

Greptile Summary

This PR improves VRF-related and PIM documentation across three files with the following enhancements:

Key Changes:

• Capitalizes acronyms (PIM, VRF, IGMP, MLD, RP, MLAG, etc.) for better readability and consistency
• Clarifies VRF-awareness status for PIM commands, documenting which parameters are truly VRF-aware vs global (addresses issue pimd/pim6d/*: Missing VRF information in "show run" #20636)
• Improves router pim command documentation, explaining it serves as a configuration container rather than enabling/disabling PIM
• Updates VRF documentation to clarify FRR's role (uses OS-provided VRF setup, doesn't create/modify VRFs)
• Corrects deprecated -n option references to use -w for VRF backend selection
• Fixes terminology throughout ("time out" → "timeout", "ipv6" → "IPv6", etc.)
• Removes repetitive VRF configuration instructions, replacing with concise "This command is VRF-aware" statements

Impact:
Documentation-only changes that improve accuracy, readability, and user expectations. No functional code changes.

Confidence Score: 5/5

• This PR is safe to merge with minimal risk as it contains only documentation improvements
• Score reflects that all changes are documentation-only with no code modifications. The updates improve accuracy, clarity, and consistency. Only one minor grammatical issue found (apostrophe in "VRF's" should be "VRFs")
• Minor fix needed in doc/user/pimv6.rst line 10 for apostrophe usage, otherwise no files require special attention

Important Files Changed

Filename	Overview
doc/user/pim.rst	Improves PIM documentation with better acronym capitalization, clearer VRF-awareness descriptions, and corrected terminology
doc/user/pimv6.rst	Improves PIMv6 documentation with similar improvements to pim.rst, but has one minor grammatical error with apostrophe usage
doc/user/zebra.rst	Clarifies VRF documentation, correctly updates deprecated -n option to -w, and explains FRR's VRF behavior more clearly

Sequence Diagram

sequenceDiagram
    participant User
    participant FRR_Docs as FRR Documentation
    participant Admin as System Admin
    participant OS as Operating System
    
    Note over User,OS: Documentation Update Flow
    
    User->>FRR_Docs: Read PIM/VRF documentation
    FRR_Docs-->>User: Shows improved, accurate info
    
    Note over FRR_Docs: Updates include:<br/>- VRF-awareness clarification<br/>- Acronym capitalization<br/>- Deprecated option updates
    
    Admin->>FRR_Docs: Check VRF configuration
    FRR_Docs-->>Admin: Clarifies FRR uses OS VRF setup<br/>(doesn't create VRFs)
    
    Admin->>OS: Creates VRF interfaces
    OS-->>Admin: VRF configured
    
    Admin->>FRR_Docs: Configure PIM parameters
    FRR_Docs-->>Admin: Shows which params are<br/>VRF-aware vs global
    
    Note over Admin,OS: Key clarification:<br/>Some PIM commands (join-prune-interval,<br/>packets, register-suppress-time)<br/>are NOT VRF-aware

Loading

[greptile-apps]

_{3 files reviewed, 1 comment}

_{Edit Code Review Agent Settings | Greptile}

[greptile-apps]

Incorrect apostrophe usage - should be VRFs (plural) not VRF's (possessive).

Suggested change

	VRF-aware and can work within the context of VRF's in order to
	VRF-aware and can work within the context of VRFs in order to

Prompt To Fix With AI

This is a comment left during a code review.
Path: doc/user/pimv6.rst
Line: 10:10

Comment:
Incorrect apostrophe usage - should be `VRFs` (plural) not `VRF's` (possessive).

```suggestion
VRF-aware and can work within the context of VRFs in order to
```

How can I resolve this? If you propose a fix, please make it concise.

[gromit1811]

greptile found another spelling issue, fixed/commit updated/force pushed

[riw777]

looks good