fix socketchannel mem leakage (#1921)

lualib/skynet/socketchannel.lua

@@ -60,6 +60,10 @@ local function close_channel_socket(self)
 	if self.__sock then
 		local so = self.__sock
 		self.__sock = false
+		if self.__wait_response then
+			skynet.wakeup(self.__wait_response)
+			self.__wait_response = nil
+		end
 		-- never raise error
 		pcall(socket.close,so[1])
 	end
@@ -128,7 +132,7 @@ local function dispatch_by_session(self)
 end
 
 local function pop_response(self)
-	while true do
+	while self.__sock do
 		local func,co = table.remove(self.__request, 1), table.remove(self.__thread, 1)
 		if func then
 			return func, co