Reduce heap allocations (#42)

* pcap: reuse Frame memory

* slog: reduce heap allocations of addresses; also prevent heap alloc of dhcp options in pcap

* dns: heapless improvement; add StackAsync buffer for more heapless operation; start thinking of errors

* reuse function for reclaiming frames among all protocols for lower memory usage

* remove extraneous code

errors.go

@@ -20,6 +20,7 @@ type errGeneric uint8
 // Generic errors common to internet functioning.
 const (
 	_                  errGeneric = iota // non-initialized err
+	ErrBug                               // lneto-bug(use build tag "debugheaplog")
 	ErrPacketDrop                        // packet dropped
 	ErrBadCRC                            // incorrect checksum
 	ErrZeroSource                        // zero source(port/addr)