ss: add more TCP_INFO components

Allow ss -i to display more TCP informations :

unacked:N   Number of un-acked packets
retrans:X/Y   X: number of outstanding retransmit packets
              Y: total number of retransmits for the session
lost:N       Number of lost packets (tcpi_lost)
sacked:N     Number of sacked packets (tcpi_sacked)
facked:N     Number of facked packets (tcpi_facked)
reordering:N Reordering level (if different of 3)

Example :

$ ss -emoi dst 10.7.7.83
tcp   ESTAB      0      1154056   10.7.7.84:54127    10.7.7.83:34342
timer:(on,200ms,0) ino:57003 sk:ffff88063c51d0c0 <->
	 skmem:(r0,rb89280,t0,tb2097152,f726504,w1436184,o0,bl0) ts sack cubic
wscale:7,6 rto:310 rtt:107.375/1 mss:1448 cwnd:568 ssthresh:108 send
61.3Mbps unacked:568 retrans:0/21 reordering:127 rcv_space:29200
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Neal Cardwell <ncardwell@google.com>

misc/ss.c

@@ -1435,6 +1435,19 @@ static void tcp_show_info(const struct nlmsghdr *nlh, struct inet_diag_msg *r,
 					 / rtt));
 		}
 
+		if (info->tcpi_unacked)
+			printf(" unacked:%u", info->tcpi_unacked);
+		if (info->tcpi_retrans || info->tcpi_total_retrans)
+			printf(" retrans:%u/%u", info->tcpi_retrans,
+			       info->tcpi_total_retrans);
+		if (info->tcpi_lost)
+			printf(" lost:%u", info->tcpi_lost);
+		if (info->tcpi_sacked && r->idiag_state != SS_LISTEN)
+			printf(" sacked:%u", info->tcpi_sacked);
+		if (info->tcpi_fackets)
+			printf(" fackets:%u", info->tcpi_fackets);
+		if (info->tcpi_reordering != 3)
+			printf(" reordering:%d", info->tcpi_reordering);
 		if (info->tcpi_rcv_rtt)
 			printf(" rcv_rtt:%g", (double) info->tcpi_rcv_rtt/1000);
 		if (info->tcpi_rcv_space)