[tcp] Update ts_recent whenever window is advanced

Commit 3f442d3 ("[tcp] Record ts_recent on first received packet")
failed to achieve its stated intention.

Fix this (and reduce the code size) by moving the ts_recent update to
tcp_rx_seq().  This is the code responsible for advancing the window,
called by both tcp_rx_syn() and tcp_rx_data(), and so the window check
is now redundant.

Reported-by: Frank Weed <zorbustheknight@gmail.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/net/tcp.c

 	 * Equivalent to RCV.WND in RFC 793 terminology.
 	 */
 	uint32_t rcv_win;
-	/** Most recent received timestamp
+	/** Received timestamp value
+	 *
+	 * Updated when a packet is received; copied to ts_recent when
+	 * the window is advanced.
+	 */
+	uint32_t ts_val;
+	/** Most recent received timestamp that advanced the window
 	 *
 	 * Equivalent to TS.Recent in RFC 1323 terminology.
 	 */
  * @v seq_len		Sequence space length to consume
  */
 static void tcp_rx_seq ( struct tcp_connection *tcp, uint32_t seq_len ) {
+
+	/* Sanity check */
+	assert ( seq_len > 0 );
+
+	/* Update acknowledgement number */
 	tcp->rcv_ack += seq_len;
+
+	/* Update window */
 	if ( tcp->rcv_win > seq_len ) {
 		tcp->rcv_win -= seq_len;
 	} else {
 		tcp->rcv_win = 0;
 	}
+
+	/* Update timestamp */
+	tcp->ts_recent = tcp->ts_val;
+
+	/* Mark ACK as pending */
 	tcp->flags |= TCP_ACK_PENDING;
 }
 
 	struct tcp_options options;
 	size_t hlen;
 	uint16_t csum;
-	uint32_t start_seq;
 	uint32_t seq;
 	uint32_t ack;
 	uint32_t win;
 	
 	/* Parse parameters from header and strip header */
 	tcp = tcp_demux ( ntohs ( tcphdr->dest ) );
-	seq = start_seq = ntohl ( tcphdr->seq );
+	seq = ntohl ( tcphdr->seq );
 	ack = ntohl ( tcphdr->ack );
 	win = ntohs ( tcphdr->win );
 	flags = tcphdr->flags;
 	tcp_rx_opts ( tcp, ( ( ( void * ) tcphdr ) + sizeof ( *tcphdr ) ),
 		      ( hlen - sizeof ( *tcphdr ) ), &options );
+	if ( options.tsopt )
+		tcp->ts_val = ntohl ( options.tsopt->tsval );
 	iob_pull ( iobuf, hlen );
 	len = iob_len ( iobuf );
 	seq_len = ( len + ( ( flags & TCP_SYN ) ? 1 : 0 ) +
 			goto discard;
 	}
 
-	/* Update timestamp, if applicable */
-	if ( options.tsopt &&
-	     tcp_in_window ( tcp->rcv_ack, start_seq, seq_len ) ) {
-		tcp->ts_recent = ntohl ( options.tsopt->tsval );
-	}
-
 	/* Enqueue received data */
 	tcp_rx_enqueue ( tcp, seq, flags, iob_disown ( iobuf ) );