[2414] Compilation fix for FreeBSD

src/lib/dhcp/memfile_lease_mgr.cc

@@ -12,6 +12,7 @@
 // OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
 // PERFORMANCE OF THIS SOFTWARE.
 
+#include <iostream>
 #include "memfile_lease_mgr.h"
 
 using namespace isc::dhcp;