allocations improvements and tunnel fixes (#1248)

* reduce allocations in tunnel code

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

* another allocation fix

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

* allocate maps with len if it known

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

* allocate key for send once

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

tunnel/listener.go

@@ -77,6 +77,8 @@ func (t *tunListener) process() {
 
 				// create a new session session
 				sess = &session{
+					// the session key
+					key: t.token + m.channel + sessionId,
 					// the id of the remote side
 					tunnel: m.tunnel,
 					// the channel