testing.B.Loop() standardization and StackAsync.Debug improvement (#156)

* testing.B.Loop() standardization and StackAsync.Debug heap debugging improvement

* apply @MDr164 fixes

* @MDr164 great suggestions to prevent panic and print correct mallocs

x/xnet/xnet_debug_pcap.go

@@ -2,7 +2,11 @@
 
 package xnet
 
-import "os"
+import (
+	"os"
+
+	"github.com/soypat/lneto/internal"
+)
 
 var _pcap CapturePrinter
 
@@ -14,4 +18,7 @@ func init() {
 
 func debugPacket(msg string, b []byte) {
 	_pcap.PrintEthernet(msg, b)
+	if internal.HeapAllocDebugging {
+		internal.LogAllocs(msg)
+	}
 }