RX_CLOSE_IDLE accounted as sc_rx_close_idle for timeout_idle hit

RX_TIMEOUT was issued when the timeout_idle was hit waiting for another
client request and accounted as an error in sess_closed_err.

We now turn this case into an RX_CLOSE_IDLE which does not get accounted
as an error.

Closes #3208

bin/varnishd/VSC_main.vsc

@@ -539,6 +539,14 @@
 
 	Number of session closes with Error RX_TIMEOUT (Receive timeout)
 
+.. varnish_vsc:: sc_rx_close_idle
+	:level:	diag
+	:oneliner:	Session Err RX_CLOSE_IDLE
+
+	Number of session closes with Error RX_CLOSE_IDLE:
+	timeout_idle has been exceeded while waiting for a
+	client request.
+
 .. varnish_vsc:: sc_tx_pipe
 	:level:	diag
 	:oneliner:	Session OK  TX_PIPE

bin/varnishd/cache/cache_session.c

@@ -424,7 +424,7 @@ ses_handle(struct waited *wp, enum wait_event ev, vtim_real now)
 
 	switch (ev) {
 	case WAITER_TIMEOUT:
-		SES_Delete(sp, SC_RX_TIMEOUT, now);
+		SES_Delete(sp, SC_RX_CLOSE_IDLE, now);
 		break;
 	case WAITER_REMCLOSE:
 		SES_Delete(sp, SC_REM_CLOSE, now);

include/tbl/sess_close.h

@@ -40,6 +40,7 @@ SESS_CLOSE(RX_BODY,	  rx_body,	1,	"Failure receiving req.body")
 SESS_CLOSE(RX_JUNK,	  rx_junk,	1,	"Received junk data")
 SESS_CLOSE(RX_OVERFLOW,   rx_overflow,	1,	"Received buffer overflow")
 SESS_CLOSE(RX_TIMEOUT,	  rx_timeout,	1,	"Receive timeout")
+SESS_CLOSE(RX_CLOSE_IDLE, rx_close_idle,0,	"timeout_idle reached")
 SESS_CLOSE(TX_PIPE,	  tx_pipe,	0,	"Piped transaction")
 SESS_CLOSE(TX_ERROR,	  tx_error,	1,	"Error transaction")
 SESS_CLOSE(TX_EOF,	  tx_eof,	0,	"EOF transmission")