Update localhost and private IP validations

[neatzsche]

Description

Prevents a node from accepting localhost peers from another peer that provides a peer address that is in the loopback address range that isn't just 127.0.0.1. Also extends isPrivate() validation to prevent accepting a link-local peer.

Checklist

• Reviewed the contributing document
• Rebased on top of master (no merge commits)
• Ran clang-format v8.0.0 (via make format or the Visual Studio extension)
• Compiles
• Ran all tests
• If change impacts performance, include supporting evidence per the performance document

[Copilot]

Pull request overview

This PR enhances the security of peer address validation by expanding localhost detection and adding link-local address filtering. The changes prevent nodes from accepting peer addresses in the full loopback range (127.x.y.z) instead of just 127.0.0.1, and also reject link-local addresses (169.254.x.y) as private addresses that should not be advertised across the network.

Changes:

• Expanded isLocalhost() to detect the entire 127.x.y.z loopback range using bit-shift validation
• Added link-local address range (169.254.x.y) to isPrivate() validation