ctdb-killtcp: Change struct ctdb_tcp_kill to store arbitrary destructor data

ctdb-killtcp: Change struct ctdb_tcp_kill to store arbitrary destructor data

The destructor used in this instances needs a CTDB context and a VNN.
However, destructors used in other cases may need different data.

For this instance create a local structure to hold the required data.

Signed-off-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Amitay Isaacs <amitay@gmail.com>