bonding: don't lock when copying/clearing VLAN list on slave

When copying VLAN information to or removing from a slave
during slave addition or removal, the bonding code currently holds
the bond->lock for write to prevent concurrent modification of the
vlan_list / vlgrp.

	This is unnecessary, as all of these operations occur under
RTNL.  Holding the bond->lock also caused might_sleep issues for
some drivers' ndo_vlan_* functions.  This patch removes the extra
locking.

	Problem reported by Michael Chan <mchan@broadcom.com>

Signed-off-by: Jay Vosburgh <fubar@us.ibm.com>
Cc: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>