brcmfmac: To fix kernel crash on out of boundary access

To truncate the additional bytes, if extra bytes have been received.
Current code only have a warning and proceed without handling it.
But in one of the crash reported by DVT, these causes the
crash intermittently. So the processing is limit to the skb->len.
Signed-off-by: Raveendran Somu <raveendran.somu@cypress.com>
Signed-off-by: Chi-hsien Lin <chi-hsien.lin@cypress.com>
Signed-off-by: Wright Feng <wright.feng@cypress.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200604071835.3842-2-wright.feng@cypress.com

drivers/net/wireless/broadcom/brcm80211/brcmfmac/fwsignal.c

@@ -1843,6 +1843,9 @@ void brcmf_fws_hdrpull(struct brcmf_if *ifp, s16 siglen, struct sk_buff *skb)
 
 	WARN_ON(siglen > skb->len);
 
+	if (siglen > skb->len)
+		siglen = skb->len;
+
 	if (!siglen)
 		return;
 	/* if flow control disabled, skip to packet data and leave */