net: bonding: constify attribute_group structures.

attribute_group are not supposed to change at runtime. All functions
working with attribute_group provided by <linux/netdevice.h> work
with const attribute_group. So mark the non-const structs as const.

File size before:
   text	   data	    bss	    dec	    hex	filename
   4512	   1472	      0	   5984	   1760	drivers/net/bonding/bond_sysfs.o

File size After adding 'const':
   text	   data	    bss	    dec	    hex	filename
   4576	   1408	      0	   5984	   1760	drivers/net/bonding/bond_sysfs.o
Signed-off-by: NArvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/bonding/bond_sysfs.c

@@ -759,7 +759,7 @@ static struct attribute *per_bond_attrs[] = {
 	NULL,
 };
 
-static struct attribute_group bonding_group = {
+static const struct attribute_group bonding_group = {
 	.name = "bonding",
 	.attrs = per_bond_attrs,
 };