net: order MPLS ethertypes numerically

All ethertypes other than ETH_P_MPLS_UC, ETH_P_MPLS_MC and
ETH_P_ATMMPOA were already ordered numerically.  This commit moves
those three ETH_P_... values into correct numerical order too.

Signed-off-by: Neil Jerram <Neil.Jerram@metaswitch.com>
Signed-off-by: David S. Miller <davem@davemloft.net>