Fix Scylla compilation with Crypto++ v6.
Fix Scylla compilation with Crypto++ v6.

In Crypto++ v6, the `byte` typedef has been moved from the global
namespace to the `CryptoPP::` namespace.

This fix brings in the CryptoPP namespace so that the `byte` typedef is
seen with both old and new versions of Crypto++.

Fixes #3252.

Signed-off-by: Vladimir Krivopalov <dc9186a06078733915a6fcbab34e59120be2b484@scylladb.com>
Message-Id: <799d055be710231884d101a52c0be8ed8b0a9806.1520125889.git.dc9186a06078733915a6fcbab34e59120be2b484@scylladb.com>

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