ss: add more tcp socket diagnostics

Display 4 additional tcp socket info fields :

backoff : exponential backoff
lastsnd : time in milli second since last send
lastrcv : time in milli second since last receive
lastack : time in milli second since last acknowledgement

$ ss -ti dst :22
State       Recv-Q Send-Q                  Local Address:Port
Peer Address:Port
ESTAB       0      0                        172.16.5.1:58470
172.17.131.143:ssh
	 cubic wscale:7,7 rto:228 rtt:30/20 ato:40 mss:1256 cwnd:6 ssthresh:4
send 2.0Mbps lastsnd:3480 lastrcv:3464 lastack:3464 rcv_rtt:81.5
rcv_space:87812
Signed-off-by: Eric Dumazet <edumazet@google.com>

misc/ss.c

@@ -1554,6 +1554,8 @@ static void tcp_show_info(const struct nlmsghdr *nlh, struct inet_diag_msg *r,
 			       info->tcpi_rcv_wscale);
 		if (info->tcpi_rto && info->tcpi_rto != 3000000)
 			printf(" rto:%g", (double)info->tcpi_rto/1000);
+		if (info->tcpi_backoff)
+			printf(" backoff:%u", info->tcpi_backoff);
 		if (info->tcpi_rtt)
 			printf(" rtt:%g/%g", (double)info->tcpi_rtt/1000,
 			       (double)info->tcpi_rttvar/1000);
@@ -1583,6 +1585,15 @@ static void tcp_show_info(const struct nlmsghdr *nlh, struct inet_diag_msg *r,
 					 / rtt));
 		}
 
+		if (info->tcpi_last_data_sent)
+			printf(" lastsnd:%u", info->tcpi_last_data_sent);
+
+		if (info->tcpi_last_data_recv)
+			printf(" lastrcv:%u", info->tcpi_last_data_recv);
+
+		if (info->tcpi_last_ack_recv)
+			printf(" lastack:%u", info->tcpi_last_ack_recv);
+
 		if (info->tcpi_pacing_rate &&
 		    info->tcpi_pacing_rate != ~0ULL) {
 			printf(" pacing_rate %sbps",