net: constify attribute_group structures.

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

File size before:
text data bss dec hex filename
9968 3168 16 13152 3360 net/core/net-sysfs.o

File size After adding 'const':
text data bss dec hex filename
10160 2976 16 13152 3360 net/core/net-sysfs.o

Signed-off-by: Arvind Yadav <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/core/net-sysfs.c

···
 };
 
 
-static struct attribute_group netstat_group = {
+static const struct attribute_group netstat_group = {
 	.name  = "statistics",
 	.attrs  = netstat_attrs,
 };
···
 	NULL
 };
 
-static struct attribute_group wireless_group = {
+static const struct attribute_group wireless_group = {
 	.name = "wireless",
 	.attrs = wireless_attrs,
 };
···
 	NULL
 };
 
-static struct attribute_group dql_group = {
+static const struct attribute_group dql_group = {
 	.name  = "byte_queue_limits",
 	.attrs  = dql_attrs,
 };