feat: add WithSettingEngineFunc ConnectOption to customize the SettingEngine

[UbiShipDev1]

Motivation

NewPCTransport builds its webrtc.SettingEngine internally with no extension point, so callers cannot influence ICE behavior beyond WithICETransportPolicy / WithDisableTURN.

We run a server-side agent co-located with the SFU on a host that has many interfaces (docker bridges, veth*, IPv6). pion gathers ICE host candidates from all of them and sometimes selects an unreachable one, silently breaking the subscriber media path (the agent goes "deaf"). The remedy is SettingEngine.SetInterfaceFilter / SetIPFilter, which the SDK doesn't expose.

Change

Adds a single, opt-in ConnectOption:

// WithSettingEngineFunc customizes the pion SettingEngine before the WebRTC
// API is constructed. Invoked for every PeerConnection (publisher + subscriber).
func WithSettingEngineFunc(fn func(*webrtc.SettingEngine)) ConnectOption

fn runs after the SDK finishes configuring the SettingEngine and before webrtc.NewAPI, so callers can layer ICE interface/IP filters, SetNAT1To1IPs, etc. without losing the SDK's own settings.

Usage:

room, err := lksdk.ConnectToRoom(url, info, cb,
    lksdk.WithSettingEngineFunc(func(se *webrtc.SettingEngine) {
        se.SetInterfaceFilter(func(name string) bool { return name == "eth0" || name == "lo" })
        se.SetIPFilter(func(ip net.IP) bool { return ip.To4() != nil })
    }),
)

Details

• signalling.ConnectParams.SettingEngineFunc carries the hook; WithSettingEngineFunc sets it (mirrors the existing option pattern).
• Threaded into both NewPCTransport calls (publisher + subscriber) and invoked in NewPCTransport just before webrtc.NewAPI.
• No behavior change when unset. Unit test included (TestWithSettingEngineFunc). go build ./... && go test green.

Happy to adjust naming or scope to fit your conventions.

🤖 Generated with Claude Code

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[cnderrauber]

looks good!

[cnderrauber]

@UbiShipDev1 could you please sign our Contributor License Agreement?