Fix me in htc.c relating to skb_reserve

Greetings Kalle, John and others,
I am wondering why this file is complaining about the code below, if someone can explain to me the issue I would be very glad :).
static struct sk_buff *ath10k_htc_build_tx_ctrl_skb(void *ar)

{
       struct sk_buff *skb;
       struct ath10k_skb_cb *skb_cb;

       skb = dev_alloc_skb(ATH10K_HTC_CONTROL_BUFFER_SIZE);
       if (!skb)
               return NULL;

  skb_reserve(skb, 20); /* FIXME: why 20 bytes? */
  WARN_ONCE((unsigned long)skb->data & 3, "unaligned skb");

  skb_cb = ATH10K_SKB_CB(skb);
  memset(skb_cb, 0, sizeof(*skb_cb));

ath10k_dbg(ar, ATH10K_DBG_HTC, "%s: skb %p\n", __func__, skb); return skb;
}