rds_rm_zerocopy_callback() uses list_add_tail() with swapped
arguments. This links the list head with the new entry, losing
the references to the remaining part of the list.

Fixes: 9426bbc6 ("rds: use list structure to track information for zerocopy completion notification")
Suggested-by: NPaolo Abeni <pabeni@redhat.com>
Signed-off-by: NPietro Borrello <borrello@diag.uniroma1.it>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>