We're currently using boost::lockfree::consume_all() to consume
smp requests, but this has two problems:
1. consume_all() calls consume_one() internally, which means it accesses
the ring index once per message
2 we interleave calling the request function with accessing the ring, which
allows the other side to access the ring again, bouncing ring cache lines.
Fix by copying all available items in one show, using pop(array), and then
processing them afterwards.
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