bonding: prevent netpoll over bonded interfaces

Support for netpoll over bonded interfaces was added here:

	commit f6dc31a8
	Author: WANG Cong <amwang@redhat.com>
	Date:   Thu May 6 00:48:51 2010 -0700

	    bonding: make bonding support netpoll

but it is bad enough that we should probably just disable netpoll over
bonding until some of the locking logic in the bonding driver is changed
or converted completely to RCU.  Simple actions like changing the active
slave in active-backup mode will hang the box if a high enough printk
debugging level is enabled.

Keeping the old code around will be good for anyone that wants to work
on it (and for after the RCU conversion), so I propose this small patch
rather than ripping it all out.

Signed-off-by: Andy Gospodarek <andy@greyhouse.net>
Signed-off-by: Jay Vosburgh <fubar@us.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>