Merge branch 'bond-bridge-xstats-json' into next

Nikolay Aleksandrov  says:

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This set adds json output support to the xstats API (patch 01) and then
adds json support to the bridge xstats output (patch 02) and adds xstats
output support (both plain text and json) for the bonding (patch 03).
It doesn't change the bridge's plain text output, but it fixes an
inconsistency that could happen if new bridge xstats attributes were
added (print the interface name once for each group of xstats attrs).

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Signed-off-by: David Ahern <dsahern@gmail.com>