cql_server::do_accepts: modernize loop
cql_server::do_accepts: modernize loop

Replace recursion in cql_server::do_accepts with more modern repeat()
from future-util.hh.

Fixes #2467.

Signed-off-by: Etienne Kruger <4f1ea4f09db2aaafb0a92c0b9e57751121ed6647@loadavg.io>
Message-Id: <20170628033130.19824-1-4f1ea4f09db2aaafb0a92c0b9e57751121ed6647@loadavg.io>

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