The problem is that you forgot to also define DBG_STRUCT_HIST,
which resulted in a broken binary - I did not cover this compilation
corner-case when I pushed the feature.
Just pushed a fix  for this on master. Defining DBG_TCPCON
without DBG_STRUCT_HIST should have no impact on the resulting
binary. You will, however, get some nice warnings all over your
screen if you try this again :)