bonding: use table for mode names

Use a small array in bond_mode_name() for the names, thus saving some
space:

before

    text     data      bss      dec    hex filename
   57736     9372      344    67452  1077c drivers/net/bonding/bonding.ko

after
    text     data      bss      dec    hex filename
   57441     9372      344    67157  10655 drivers/net/bonding/bonding.ko

Signed-off-by: Holger Eitzenberger <holger@eitzenberger.org>
Signed-off-by: David S. Miller <davem@davemloft.net>