Tcp buffer bug fix (#79)

* start working on tracking down tcp buffer bug

* mtu refactor

* modularize test

* more precise testing

* tests fail, but is it the failure we are looking for?

* fix typo in espradio link (#76)

* implement a new backoff abstraction (#75)

* rewrite backoff api

* rewrite tcp.Conn.Write

* keep fixing small things

* much better Conn.Read implementation

* fix critical overflow bug in internal.ConnRWBackoff

---------

Co-authored-by: Joel Wetzell <jwetzell@yahoo.com>

definitions.go

@@ -1,7 +1,5 @@
 package lneto
 
-import "time"
-
 // StackNode is an abstraction of a packet exchanging protocol controller. This is the building block for all protocols,
 // from Ethernet to IP to TCP, practically any protocol can be expressed as a StackNode and function completely.
 // Today protocols represented by StackNode also include NTP, DNS, DHCP, ARP, ICMP, UDP, mDNS.
@@ -39,12 +37,6 @@ type StackNode interface {
 	// SetFlagPending(flagPending func(numPendingEncapsulations int))
 }
 
-// BackoffStrategy is the abstraction of a backoff strategy for retrying an operation.
-// It returns the amount of time to sleep for. If returned value is 0 then runtime.Gosched is called.
-// A negative value results in no action taken.
-// consecutiveBackoffs starts at 1 and increments by 1 every time the operation is retried.
-type BackoffStrategy func(consecutiveBackoffs int) (sleep time.Duration)
-
 // IPProto represents the IP protocol number.
 type IPProto uint8