test: Make udev_properties array fixed-size.

The udev_properties array is currently variable length, which causes the tests to invoke undefined behavior on empty lists, as it attempts to access the first array item to check if the key is NULL, which is an out of bounds read and will fail when the struct alignment happens to line up such that there is no padding after the list in the empty list case.

By making the udev_properties array 32 items long, it can encapsulate every existing case, with only a fairly small amount of memory overhead, and without requiring every single TEST_DEVICE call to initialize udev_properties.