drivers/net: const-ify ethtool_ops declarations

drivers/net/3c501.c

drivers/net/3c501.h

drivers/net/3c503.c

drivers/net/3c505.c

drivers/net/3c507.c

drivers/net/3c509.c

drivers/net/3c515.c

drivers/net/3c523.c

drivers/net/3c527.c

drivers/net/3c59x.c

drivers/net/8139cp.c

drivers/net/8139too.c

drivers/net/acenic.c

drivers/net/amd8111e.c

drivers/net/arm/at91_ether.c

drivers/net/arm/etherh.c

drivers/net/au1000_eth.c

drivers/net/b44.c

drivers/net/bnx2.c

drivers/net/bonding/bond_main.c