session: avoid unnecessary timeouts

When a slow operation is running on the HSM (like a RSA key generation
>= 3072), the HSM will be busy for more than the session timeout of
30seconds.

Although the device did not reply within timeout, it did not discard the
session, and we should not either. This bumps the last_active when we
receive a reply from the HSM.

src/session.rs

@@ -225,6 +225,7 @@ impl Session {
                 return Err(e.into());
             }
         };
+        self.last_active = Instant::now();
 
         if response.is_err() {
             session_error!(self, "uuid={} error={:?}", &uuid, response.code);