Revert "net: bonding: fix error return code of bond_neigh_init()"

commit 080bfa1e upstream.

This reverts commit 2055a99d.

This change rejects legitimate configurations.

A slave doesn't need to exist nor implement ndo_slave_setup.

Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>