net/bonding: Enforce active-backup policy for IPoIB bonds

net/bonding: Enforce active-backup policy for IPoIB bonds

When using an IPoIB bond currently only active-backup mode is a valid
use case and this commit strengthens it.

Since commit 3c068e50463a ("net/bonding: Enable bonding to enslave
netdevices not supporting set_mac_address()") was introduced till
4.7-rc1, IPoIB didn't support the set_mac_address ndo, and hence the
fail over mac policy always applied to IPoIB bonds.

With the introduction of commit 620782957f98 ("IB/IPoIB: Allow setting
the device address"), that doesn't hold and practically IPoIB bonds are
broken as of that. To fix it, lets go to fail over mac if the device
doesn't support the ndo OR this is IPoIB device.

As a by-product, this commit also prevents a stack corruption which
occurred when trying to copy 20 bytes (IPoIB) device address
to a sockaddr struct that has only 16 bytes of storage.

Signed-off-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Acked-by: Andy Gospodarek <gospo@cumulusnetworks.com>
Signed-off-by: Jay Vosburgh <jay.vosburgh@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>