Don't populate the array modes on the stack but instead make it
static const. Makes the object code smaller by 303 bytes.

Before:
   text	   data	    bss	    dec	    hex	filename
  51240	   5008	   1312	  57560	   e0d8 mellanox/mlx4/en_ethtool.o

After:
   text	   data	    bss	    dec	    hex	filename
  50937	   5008	   1312	  57257	   dfa9	mellanox/mlx4/en_ethtool.o

(gcc version 9.2.1, amd64)
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>