Merge branch 'net-add-and-use-function-dev_fetch_sw_netstats-for-fetching-pcpu_sw_netstats'

Heiner Kallweit says:

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net: add and use function dev_fetch_sw_netstats for fetching pcpu_sw_netstats

In several places the same code is used to populate rtnl_link_stats64
fields with data from pcpu_sw_netstats. Therefore factor out this code
to a new function dev_fetch_sw_netstats().
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Signed-off-by: Jakub Kicinski <kuba@kernel.org>