tcp: completed trace functions

tcp: completed trace functions

* Populated the trace struct that weren't used before
* Modified and created format functions to format tcp packets and
connections
* Completed the node definitions to add the format_trace function
* Filled the tracing parts with `vlib_add_trace' calls in each tcp node
function

For the nodes in tcp_input.c, there is a verbose trace and a non-verbose
trace. Each packet goes through tcp[4-6]-input which is traced with
`format_tcp_rx_trace', and the other nodes are traced with
`format_tcp_rx_trace_short'.

Change-Id: I4f2eed023f5973c14343132a33b06131cf063aa2
Signed-off-by: Pierre Pfister <ppfister@cisco.com>
Signed-off-by: Clement Durand <clement.durand@polytechnique.edu>