bonding: fix multiple module load problem

bonding: fix multiple module load problem

Some users still load bond module multiple times to create bonding
devices.  This accidentally was broken by a later patch about
the time sysfs was fixed.  According to Jay, it was broken
by:
   commit 2f7779391a34a88d5af38c16f18560637d5f8d85
   Author: Jay Vosburgh <fubar@us.ibm.com>
   Date:   Fri Jun 13 18:12:04 2008 -0700

     bonding: Allow setting max_bonds to zero

Note: sysfs and procfs still produce WARN() messages when this is done
so the sysfs method is the recommended API.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: Jay Vosburgh <fubar@us.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>