Add configurable so_linger parameter for TCP and TLS links

[Copilot]

The TCP/TLS linger timeout was hardcoded to 10 seconds with no way to configure it per-session or per-locator. This adds so_linger as a first-class session/endpoint config option, consistent with so_rcvbuf/so_sndbuf patterns.

Changes

Config schema (zenoh-config)

• Added TcpConf { so_linger: Option<i32> } under transport.link.tcp
• Added so_linger: Option<i32> to existing TLSConf

TCP link (zenoh-link-tcp)

• Added TCP_SO_LINGER endpoint config key constant
• Added TcpConfigurator implementing ConfigurationInspector<Config> — translates session-level so_linger into endpoint config (parallel to TlsConfigurator)
• LinkUnicastTcp::new() now takes linger: Option<Duration>; get_so_linger() reads from endpoint config, falling back to TCP_LINGER_TIMEOUT
• accept_task receives linger value captured from the listener endpoint

TLS link (zenoh-link-tls)

• Same pattern: TLS_SO_LINGER constant, TlsConfigurator updated to emit it, LinkUnicastTls::new() and accept_task updated accordingly

Link orchestration (zenoh-link)

• Registered TcpConfigurator in LinkConfigurator::configurations() so TCP session config propagates to endpoint config at session open time

Docs

• Updated DEFAULT_CONFIG.json5 with commented-out so_linger entries in tcp and tls sections

Usage

Session config:

{
  transport: { link: { tcp: { so_linger: 5 } } }
}

Endpoint locator (overrides session config):

tcp/127.0.0.1:7447#so_linger=5

A negative value (e.g. -1) disables SO_LINGER. Unset defaults to 10 s (existing TCP_LINGER_TIMEOUT).

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• 224.0.0.1
  • Triggering command: REDACTED, pid is -1 (packet block)
• 224.0.0.224
  • Triggering command: REDACTED, pid is -1 (packet block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

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