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 <arvind.yadav.cs@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/net-sysfs.c

@@ -626,7 +626,7 @@ static struct attribute *netstat_attrs[] = {
 };
 
 
-static struct attribute_group netstat_group = {
+static const struct attribute_group netstat_group = {
 	.name  = "statistics",
 	.attrs  = netstat_attrs,
 };
@@ -636,7 +636,7 @@ static struct attribute *wireless_attrs[] = {
 	NULL
 };
 
-static struct attribute_group wireless_group = {
+static const struct attribute_group wireless_group = {
 	.name = "wireless",
 	.attrs = wireless_attrs,
 };
@@ -1204,7 +1204,7 @@ static struct attribute *dql_attrs[] = {
 	NULL
 };
 
-static struct attribute_group dql_group = {
+static const struct attribute_group dql_group = {
 	.name  = "byte_queue_limits",
 	.attrs  = dql_attrs,
 };