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>