Address reviewer's comments floodlight/loxigen#297

Reference:
https://github.com/floodlight/loxigen/pull/297
diff --git a/java_gen/pre-written/src/test/java/org/projectfloodlight/openflow/types/IPv4AddressTest.java b/java_gen/pre-written/src/test/java/org/projectfloodlight/openflow/types/IPv4AddressTest.java
index 2e6128e..0716b50 100644
--- a/java_gen/pre-written/src/test/java/org/projectfloodlight/openflow/types/IPv4AddressTest.java
+++ b/java_gen/pre-written/src/test/java/org/projectfloodlight/openflow/types/IPv4AddressTest.java
@@ -281,24 +281,20 @@
 
         IPv4AddressWithMask v;
 
-        v = original.withMask(expectedMask);
+        v = original.withMask(IPv4Address.of(new byte[] {-1, -1, -1, 0}));
         assertEquals(v.getValue(), expectedValue);
         assertEquals(v.getMask(), expectedMask);
 
-        v = original.withMask(new byte[] {-1, -1, -1, 0});
+        v = original.withMask(IPv4Address.of(0xFFFF_FF00));
         assertEquals(v.getValue(), expectedValue);
         assertEquals(v.getMask(), expectedMask);
 
-        v = original.withMask(0xFFFF_FF00);
-        assertEquals(v.getValue(), expectedValue);
-        assertEquals(v.getMask(), expectedMask);
-
-        v = original.withMask("255.255.255.0");
+        v = original.withMask(IPv4Address.of("255.255.255.0"));
         assertEquals(v.getValue(), expectedValue);
         assertEquals(v.getMask(), expectedMask);
 
         Inet4Address i4a = (Inet4Address) InetAddress.getByName("255.255.255.0");
-        v = original.withMask(i4a);
+        v = original.withMask(IPv4Address.of(i4a));
         assertEquals(v.getValue(), expectedValue);
         assertEquals(v.getMask(), expectedMask);