core: ivshmem: Fix cell disconnection

core: ivshmem: Fix cell disconnection

Move the disconnect call before the potential endpoint copy operation.
Otherwise we risk to update the stale second entry, not the now active
first one.

This change also ensures that disconnect is performed even for the last
endpoint. This will allow us to put cleanup tasks into that function
that have to be executed unconditionally.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>