ss: display pacing_rate/max_pacing_rate

Since linux-3.15, kernel exports tcpi_pacing_rate and
tcpi_max_pacing_rate in tcp_info

Add TCP pacing_rate information on ss -i output :

lpaa23:~# ./ss -ti dst 10.246.7.151
State      Recv-Q Send-Q   Local Address:Port       Peer Address:Port
ESTAB      0      325800    10.246.7.151:57614
10.246.7.152:46811
	 cubic wscale:7,7 rto:201 rtt:0.081/0.006 mss:1448 cwnd:90 ssthresh:63
send 12871.1Mbps pacing_rate 15397.8Mbps unacked:90 retrans:0/305
rcv_space:29200

If SO_MAX_PACING_RATE is set on the socket, we add /max_pacing_rate as
in :

... pacing_rate 1570.5Mbps/2.0Gbps ...
Signed-off-by: Eric Dumazet <edumazet@google.com>

misc/ss.c

@@ -1583,6 +1583,16 @@ static void tcp_show_info(const struct nlmsghdr *nlh, struct inet_diag_msg *r,
 					 / rtt));
 		}
 
+		if (info->tcpi_pacing_rate &&
+		    info->tcpi_pacing_rate != ~0ULL) {
+			printf(" pacing_rate %sbps",
+				sprint_bw(b1, info->tcpi_pacing_rate * 8.));
+
+			if (info->tcpi_max_pacing_rate &&
+			    info->tcpi_max_pacing_rate != ~0ULL)
+				printf("/%sbps",
+					sprint_bw(b1, info->tcpi_max_pacing_rate * 8.));
+		}
 		if (info->tcpi_unacked)
 			printf(" unacked:%u", info->tcpi_unacked);
 		if (info->tcpi_retrans || info->tcpi_total_retrans)