Merge branch 'net-optmem_max-changes'

Eric Dumazet says:

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net: optmem_max changes

optmem_max default value is too small for tx zerocopy workloads.

First patch increases default from 20KB to 128 KB,
which is the value we have used for seven years.

Second patch makes optmem_max sysctl per netns.

Last patch tweaks two tests accordingly.
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Signed-off-by: David S. Miller <davem@davemloft.net>