bonding: Fix use after free in unregister path

bonding: Fix use after free in unregister path

	The following patch (based on a patch from Stephen Hemminger
<shemminger@linux-foundation.org>) removes use after free conditions in
the unregister path for the bonding master.  Without this patch, an
operation of the form "echo -bond0 > /sys/class/net/bonding_masters"
would trigger a NULL pointer dereference in sysfs.  I was not able to
induce the failure with the non-sysfs code path, but for consistency I
updated that code as well.

	I also did some testing of the bonding /proc file being open
while the bond is being deleted, and didn't see any problems there.

Signed-off-by: Jay Vosburgh <fubar@us.ibm.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>