brcmfmac: increment hard_header_len instead of overriding

In brcmf_net_attach() the hard_header_len is set to sum of ETH_HLEN
and the headroom needed by the bus interface. Better use increment
instead as hard_header_len is already initialized upon alloc_netdev().
Reviewed-by: Hante Meuleman <meuleman@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

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

@@ -640,7 +640,7 @@ int brcmf_net_attach(struct brcmf_if *ifp, bool rtnl_locked)
 	/* set appropriate operations */
 	ndev->netdev_ops = &brcmf_netdev_ops_pri;
 
-	ndev->hard_header_len = ETH_HLEN + drvr->hdrlen;
+	ndev->hard_header_len += drvr->hdrlen;
 	ndev->ethtool_ops = &brcmf_ethtool_ops;
 
 	drvr->rxsz = ndev->mtu + ndev->hard_header_len +