test: qemuxml2argv: Mock virMemoryMaxValue to remove 32/64 bit difference

Always return LLONG_MAX even on 32 bit systems. The limitation
originates from our use of "unsigned long" in several APIs. The internal
data type is unsigned long long. Make the test suite deterministic by
removing the architecture difference.

Flaw was introduced in 645881139b3d2c86acf9d644c3a1471520bc9e57 where
I've added a test that uses too large numbers.

src/util/virutil.c

@@ -2658,6 +2658,8 @@ virMemoryLimitIsSet(unsigned long long value)
  * @capped: whether the value must fit into unsigned long
  *   (long long is assumed otherwise)
  *
+ * Note: This function is mocked in tests/qemuxml2argvmock.c for test stability
+ *
  * Returns the maximum possible memory value in bytes.
  */
 unsigned long long

tests/qemuxml2argvmock.c

@@ -74,3 +74,13 @@ virTPMCreateCancelPath(const char *devpath)
 
     return path;
 }
+
+/**
+ * Large values for memory would fail on 32 bit systems, despite having
+ * variables that support it.
+ */
+unsigned long long
+virMemoryMaxValue(bool capped ATTRIBUTE_UNUSED)
+{
+    return LLONG_MAX;
+}