brcmfmac: Fix ifidx for rx data by msgbuf.

The ifidx provided by FW needs to be offsetted when receiving data
packets.

Cc: stable@vger.kernel.org # v3.17, v3.18
Reviewed-by: NArend Van Spriel <arend@broadcom.com>
Reviewed-by: NPieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: NHante Meuleman <meuleman@broadcom.com>
Signed-off-by: NArend van Spriel <arend@broadcom.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

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

@@ -1080,8 +1080,17 @@ brcmf_msgbuf_rx_skb(struct brcmf_msgbuf *msgbuf, struct sk_buff *skb,
 {
 	struct brcmf_if *ifp;
 
+	/* The ifidx is the idx to map to matching netdev/ifp. When receiving
+	 * events this is easy because it contains the bssidx which maps
+	 * 1-on-1 to the netdev/ifp. But for data frames the ifidx is rcvd.
+	 * bssidx 1 is used for p2p0 and no data can be received or
+	 * transmitted on it. Therefor bssidx is ifidx + 1 if ifidx > 0
+	 */
+	if (ifidx)
+		(ifidx)++;
 	ifp = msgbuf->drvr->iflist[ifidx];
 	if (!ifp || !ifp->ndev) {
+		brcmf_err("Received pkt for invalid ifidx %d\n", ifidx);
 		brcmu_pkt_buf_free_skb(skb);
 		return;
 	}