Enable splice for freedom outbound (downlink only)

- Add outbound name
- Add outbound conn in ctx
- Refactor splice: it can be turn on from all inbounds and outbounds
- Refactor splice: Add splice copy to vless inbound
- Fix http error test
- Add freedom splice toggle via env var
- Populate outbound obj in context
- Use CanSpliceCopy to mark a connection
- Turn off splice by default

proxy/blackhole/blackhole.go

@@ -8,6 +8,7 @@ import (
 	"time"
 
 	"github.com/xtls/xray-core/common"
+	"github.com/xtls/xray-core/common/session"
 	"github.com/xtls/xray-core/transport"
 	"github.com/xtls/xray-core/transport/internet"
 )
@@ -30,6 +31,11 @@ func New(ctx context.Context, config *Config) (*Handler, error) {
 
 // Process implements OutboundHandler.Dispatch().
 func (h *Handler) Process(ctx context.Context, link *transport.Link, dialer internet.Dialer) error {
+	outbound := session.OutboundFromContext(ctx)
+	if outbound != nil {
+		outbound.Name = "blackhole"
+	}
+	
 	nBytes := h.response.WriteTo(link.Writer)
 	if nBytes > 0 {
 		// Sleep a little here to make sure the response is sent to client.