Don't call tcp_state_change() when initializing a tcpcb, since obviously
the t_state initialization there doesn't correspond to a TCP state
change.
Add a comment explaining the usage of tcp_state_change().
- Provide string representations of TCP states.
- Use 0 instead of -1 to represent "null" sequence values.
- Include definitions of some previously omitted tcpsinfo_t fields.
- Add a tranlator for int -> tcplsinfo_t.