Merge branch 'gro-micro-optimize-dev_gro_receive'

Alexander Lobakin says:

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gro: micro-optimize dev_gro_receive()

This random series addresses some of suboptimal constructions used
in the main GRO entry point.
The main body is gro_list_prepare() simplification and pointer usage
optimization in dev_gro_receive() itself. Being mostly cosmetic, it
gives like +10 Mbps on my setup to both TCP and UDP (both single- and
multi-flow).

Since v1 [0]:
 - drop the replacement of bucket index calculation with
   reciprocal_scale() since it makes absolutely no sense (Eric);
 - improve stack usage in dev_gro_receive() (Eric);
 - reverse the order of patches to avoid changes superseding.

[0] https://lore.kernel.org/netdev/20210312162127.239795-1-alobakin@pm.me
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Signed-off-by: David S. Miller <davem@davemloft.net>