brcmfmac: Ensure pointer correctly set if skb data location changes

BugLink: http://bugs.launchpad.net/bugs/1691418

commit 455a1eb4 upstream.

The incoming skb header may be resized if header space is
insufficient, which might change the data adddress in the skb.
Ensure that a cached pointer to that data is correctly set by
moving assignment to after any possible changes.
Signed-off-by: James Hughes <james.hughes@raspberrypi.org>
Acked-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Signed-off-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

drivers/net/wireless/brcm80211/brcmfmac/core.c

@@ -211,7 +211,7 @@ static netdev_tx_t brcmf_netdev_start_xmit(struct sk_buff *skb,
 	int ret;
 	struct brcmf_if *ifp = netdev_priv(ndev);
 	struct brcmf_pub *drvr = ifp->drvr;
-	struct ethhdr *eh = (struct ethhdr *)(skb->data);
+	struct ethhdr *eh;
 
 	brcmf_dbg(DATA, "Enter, idx=%d\n", ifp->bssidx);
 
@@ -257,6 +257,8 @@ static netdev_tx_t brcmf_netdev_start_xmit(struct sk_buff *skb,
 		goto done;
 	}
 
+	eh = (struct ethhdr *)(skb->data);
+
 	if (eh->h_proto == htons(ETH_P_PAE))
 		atomic_inc(&ifp->pend_8021x_cnt);