[2902] Include in_systm.h when ip.h is included.

If in_systm.h is not included before ip.h it will cause compilation error
on NetBSD and OpenBSD. Compiler will complain that n_time is undefined
but used in ip.h.

src/lib/dhcp/protocol_util.cc

@@ -13,9 +13,13 @@
 // PERFORMANCE OF THIS SOFTWARE.
 
 #include <asiolink/io_address.h>
-#include <dhcp/dhcp6.h> // defines HWTYPE_ETHERNET
+#include <dhcp/dhcp6.h>
 #include <dhcp/protocol_util.h>
 #include <boost/static_assert.hpp>
+// in_systm.h is required on some some BSD systems
+// complaining that n_time is undefined but used
+// in ip.h.
+#include <netinet/in_systm.h>
 #include <netinet/ip.h>
 
 using namespace isc::asiolink;

src/lib/dhcp/tests/protocol_util_unittest.cc

@@ -18,9 +18,11 @@
 #include <dhcp/hwaddr.h>
 #include <dhcp/protocol_util.h>
 #include <util/buffer.h>
-
 #include <gtest/gtest.h>
-
+// in_systm.h is required on some some BSD systems
+// complaining that n_time is undefined but used
+// in ip.h.
+#include <netinet/in_systm.h>
 #include <netinet/ip.h>
 
 using namespace isc;