Convert the migration of the struct tcpcb to use a VMStateDescription,
the rest of it will come later.
Mostly mechanical, except for conversion of some 'char' to uint8_t
to ensure portability.
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com> Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org> Reviewed-by: Juan Quintela <quintela@redhat.com> Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>