tcp: need default in switch statement for enum.

[imp]

This will fix the compiler complaints. Is nothing the right thing to do when we don't know the type? Or is this an artifact of how the type is defined where the compiler thinks its a simple enum, when in fact it isn't....

[rscheff]

Apparently I've only checked clang or gccc12 but ont gcc13 - where there are subtle differences in what these compilers consider acceptable;

e.g. clang is fine with impicit typecast from enum to int32, but gcc13 isn't; but once the type is enum, locally my compiler (don't really know if its using gcc12 or clang) accept it without a default clause, but the CI compile jobs fail (and I don't know why this isn't the case locally).