hw/net/rocker: Avoid variable length array

Replace an on-stack variable length array in of_dpa_ig() with
a g_autofree heap allocation.

The codebase has very few VLAs, and if we can get rid of them all we
can make the compiler error on new additions.  This is a defensive
measure against security bugs where an on-stack dynamic allocation
isn't correctly size-checked (e.g.  CVE-2021-3527).

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Francisco Iglesias <frasse.iglesias@gmail.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

hw/net/rocker/rocker_of_dpa.c

@@ -1043,7 +1043,7 @@ static void of_dpa_flow_ig_tbl(OfDpaFlowContext *fc, uint32_t tbl_id)
 static ssize_t of_dpa_ig(World *world, uint32_t pport,
                          const struct iovec *iov, int iovcnt)
 {
-    struct iovec iov_copy[iovcnt + 2];
+    g_autofree struct iovec *iov_copy = g_new(struct iovec, iovcnt + 2);
     OfDpaFlowContext fc = {
         .of_dpa = world_private(world),
         .in_pport = pport,