fix(kcp): enable congestion control, add FEC, and fix remote node UDP diagnosis

- KCP: switch from fast3 to fast2 mode, enable FEC (10/3), enable
  congestion control (nc=0) for automatic rate adaptation
- go-gost/x: support kcp.nc metadata to override mode-initialized
  NoCongestion value in dialer and listener Init()
- Diagnosis: add udpPingViaRemoteNode, fix pingViaRemoteNode to
  dispatch based on protocol, add Protocol field to federation
  diagnose request structs

go-gost/x/dialer/kcp/dialer.go

@@ -11,6 +11,7 @@ import (
 	"github.com/go-gost/core/logger"
 	md "github.com/go-gost/core/metadata"
 	kcp_util "github.com/go-gost/x/internal/util/kcp"
+	mdutil "github.com/go-gost/x/metadata/util"
 	"github.com/go-gost/x/registry"
 	"github.com/xtaci/kcp-go/v5"
 	"github.com/xtaci/smux"
@@ -48,6 +49,9 @@ func (d *kcpDialer) Init(md md.Metadata) (err error) {
 	}
 
 	d.md.config.Init()
+	if md != nil && md.IsExists("kcp.nc") {
+		d.md.config.NoCongestion = mdutil.GetInt(md, "kcp.nc")
+	}
 
 	return nil
 }

go-gost/x/listener/kcp/listener.go

@@ -15,6 +15,7 @@ import (
 	limiter_wrapper "github.com/go-gost/x/limiter/traffic/wrapper"
 	metrics "github.com/go-gost/x/metrics/wrapper"
 	stats "github.com/go-gost/x/observer/stats/wrapper"
+	mdutil "github.com/go-gost/x/metadata/util"
 	"github.com/go-gost/x/registry"
 	"github.com/xtaci/kcp-go/v5"
 	"github.com/xtaci/smux"
@@ -53,6 +54,9 @@ func (l *kcpListener) Init(md md.Metadata) (err error) {
 
 	config := l.md.config
 	config.Init()
+	if md != nil && md.IsExists("kcp.nc") {
+		config.NoCongestion = mdutil.GetInt(md, "kcp.nc")
+	}
 
 	var conn net.PacketConn
 	if config.TCP {