// Test basic AccECN negotiation, late option enable

`./defaults.sh
sysctl -q net.ipv4.tcp_ecn=3
`

    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 4
+.002 ... 0.052 connect(4, ..., ...) = 0

+.002 > SEWA 0:0(0) <mss 1460,sackOK,TS val 100 ecr 0,nop,wscale 8>
+0.05 < SW. 0:0(0) ack 1 win 32767 <mss 1460,nop,nop,sackOK,nop,wscale 8>
+.002 > [ect0] W. 1:1(0) ack 1

+0.01 write(4, ..., 1000) = 1000
+.002 > [ect0] EAP. 1:1001(1000) ack 1
+.05 < [ect0] EAP. 1:1(0) ack 1001 win 256 <ECN e0b 1001 ceb 0 e1b 1,nop>

+0.01 %{ assert tcpi_delivered_ce == 0, tcpi_delivered_ce }%

+0.01 write(4, ..., 1000) = 1000
+.002 > [ect0] EAP. 1001:2001(1000) ack 1 <ECN e1b 1 ceb 0 e0b 1,nop>

+0.01 %{ assert tcpi_delivered_ce == 0, tcpi_delivered_ce }%