ss: group DCTCP socket statistics

ss: group DCTCP socket statistics

Keep ss output consistent and format DCTCP socket statistics similar to skmen
and timer where a group of logical values are grouped by brackets. This makes
parser scripts *and* humans more happy.

Current output of 'ss -inetm dst :80':
ESTAB       0      0 192.168.11.14:55511 173.194.66.189:443
        timer:(keepalive,14sec,0) uid:1000 ino:428768
        sk:ffff88020ceb5b00 <-> skmem:(r0,rb372480,t0,tb87040,f0,w0,o0,bl0)
        ts sack wscale:7,7 rto:250 rtt:49.225/20.837 ato:40 mss:1408 cwnd:10
        ce_state 23 alpha 23 ab_ecn 23 ab_tot 23 send 2.3Mbps
        lastsnd:121026 lastrcv:121026 lastack:30850 pacing_rate 4.6Mbps
        retrans:0/2 rcv_rtt:40.416 rcv_space:2920

New grouped output:
ESTAB       0      0 192.168.11.14:55511 173.194.66.189:443
        timer:(keepalive,14sec,0) uid:1000 ino:428768
        sk:ffff88020ceb5b00 <-> skmem:(r0,rb372480,t0,tb87040,f0,w0,o0,bl0)
        ts sack wscale:7,7 rto:250 rtt:49.225/20.837 ato:40 mss:1408 cwnd:10
        dctcp(ce_state:23,alpha:23,ab_ecn:23,ab_tot:23) send 2.3Mbps
        lastsnd:121026 lastrcv:121026 lastack:30850 pacing_rate 4.6Mbps
        retrans:0/2 rcv_rtt:40.416 rcv_space:2920

Cc: Stephen Hemminger <stephen@networkplumber.org>
Acked-by: Daniel Borkmann <dborkman@redhat.com>
Acked-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>