repair: Futurize row_buf_csum
repair: Futurize row_buf_csum

To prevent stall when number of rows inside row buf is large.

scylladb/scylla,avikivity/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla