Remove duplicate slow protocol define in bond_3ad.h

ETH_P_SLOW is already defined in include/linux/if_ether.h.
There's no need to define BOND_ETH_P_LACPDU in drivers/net/bonding/bond_3ad.h

Signed-off-by: Richard Genoud <richard.genoud@gmail.com>
Signed-off-by: Jiri Pirko <jpirko@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>