Inject CryptoPP namespace where Crypto++ `byte` typedef is used.
Inject CryptoPP namespace where Crypto++ `byte` typedef is used.

In Crypto++ v6, the `byte` typedef has been moved from the global
namespace to the CryptoPP:: namespace.
To make Scylla code compile with both old and new versions, bring the
namespace in so that the code works regardless of the scope of `byte`
definition.

Fixes #3252

Signed-off-by: Vladimir Krivopalov <dc9186a06078733915a6fcbab34e59120be2b484@scylladb.com>
Message-Id: <60e7bfe868b778b1c9bbe15d7247db64b61bd406.1520272198.git.dc9186a06078733915a6fcbab34e59120be2b484@scylladb.com>

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