net/bonding: correctly proxy slave neigh param setup ndo function

The current implemenation was buggy for slaves who use ndo_neigh_setup,
since the networking stack invokes the bonding device ndo entry (from
neigh_params_alloc) before any devices are enslaved, and the bonding
driver can't further delegate the call at that point in time. As a
result when bonding IPoIB devices, the neigh_cleanup hasn't been called.

Fix that by deferring the actual call into the slave ndo_neigh_setup
from the time the bonding neigh_setup is called.

Signed-off-by: Shlomo Pongratz <shlomop@mellanox.com>
Signed-off-by: Jay Vosburgh <fubar@us.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>