sstables: print invalid boundary type as unsigned int
sstables: print invalid boundary type as unsigned int

Otherwise it prints a binary value to the log and corrupting it.
Seen when testing scrub with randomly-corrupted sstable
using scrub_with_one_node_expect_data_loss_test
as of https://github.com/scylladb/scylla-dtest/pull/1414

Signed-off-by: Benny Halevy <23c997c90eb8537635e9392d48e7af1bf1b2ca22@scylladb.com>
Message-Id: <20200407055617.1045977-1-23c997c90eb8537635e9392d48e7af1bf1b2ca22@scylladb.com>

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