net: Allocating Large sized arrays to heap

nc_sendv_compat has a huge stack usage of 69680 bytes approx.
Moving large arrays to heap to reduce stack usage.
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: NPooja Dhannawat <dhannawatpooja1@gmail.com>
Signed-off-by: NJason Wang <jasowang@redhat.com>

net/net.c

@@ -683,23 +683,28 @@ ssize_t qemu_send_packet_raw(NetClientState *nc, const uint8_t *buf, int size)
 static ssize_t nc_sendv_compat(NetClientState *nc, const struct iovec *iov,
                                int iovcnt, unsigned flags)
 {
-    uint8_t buf[NET_BUFSIZE];
+    uint8_t *buf = NULL;
     uint8_t *buffer;
     size_t offset;
+    ssize_t ret;
 
     if (iovcnt == 1) {
         buffer = iov[0].iov_base;
         offset = iov[0].iov_len;
     } else {
+        buf = g_new(uint8_t, NET_BUFSIZE);
         buffer = buf;
-        offset = iov_to_buf(iov, iovcnt, 0, buf, sizeof(buf));
+        offset = iov_to_buf(iov, iovcnt, 0, buf, NET_BUFSIZE);
     }
 
     if (flags & QEMU_NET_PACKET_FLAG_RAW && nc->info->receive_raw) {
-        return nc->info->receive_raw(nc, buffer, offset);
+        ret = nc->info->receive_raw(nc, buffer, offset);
     } else {
-        return nc->info->receive(nc, buffer, offset);
+        ret = nc->info->receive(nc, buffer, offset);
     }
+
+    g_free(buf);
+    return ret;
 }
 
 ssize_t qemu_deliver_packet_iov(NetClientState *sender,