[master] Added missing header (Solaris compilation fix)

src/lib/dhcp/addr_utilities.cc

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