wgengine/wglog: add TS_DEBUG_RAW_WGLOG envknob for raw wg logs

Updates #7617 (part of debugging it)

Change-Id: I1bcbdcf0f929e3bcf83f244b1033fd438aa6dac1
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

wgengine/wglog/wglog.go

@@ -10,6 +10,7 @@ import (
 	"sync"
 
 	"github.com/tailscale/wireguard-go/device"
+	"tailscale.com/envknob"
 	"tailscale.com/syncs"
 	"tailscale.com/types/key"
 	"tailscale.com/types/logger"
@@ -87,6 +88,9 @@ func NewLogger(logf logger.Logf) *Logger {
 		}
 		logf(format, newargs...)
 	}
+	if envknob.Bool("TS_DEBUG_RAW_WGLOG") {
+		wrapper = logf
+	}
 	ret.DeviceLogger = &device.Logger{
 		Verbosef: logger.WithPrefix(wrapper, prefix+"[v2] "),
 		Errorf:   logger.WithPrefix(wrapper, prefix),