soccr/tcp: Introduce blob with connection info and getter for it

As an API for dumping and restoring the data the structure
with __u32-s is used. Getting one (and restoring) also involve
the size of the structure so that both -- caller and library --
can know which "version" of it the other one is using.

As a starting point all the fields that tcp_entry carries are
used.

Also note, that only tcp connection info is handled by the
library. Stuff like addresses and ports, socket options and
other are left for the caller to care for.

Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>