Merge branch 'net-attribute_group-const'

Arvind Yadav says:

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constify net attribute_group structures.

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

Signed-off-by: David S. Miller <davem@davemloft.net>