[SK_BUFF]: Introduce skb_mac_header()

For the places where we need a pointer to the mac header, it is still legal to
touch skb->mac.raw directly if just adding to, subtracting from or setting it
to another layer header.

This one also converts some more cases to skb_reset_mac_header() that my
regex missed as it had no spaces before nor after '=', ugh.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
index 053147a..a3e3d9e 100644
--- a/net/ipv6/ndisc.c
+++ b/net/ipv6/ndisc.c
@@ -828,7 +828,8 @@
 		if (ifp->flags & (IFA_F_TENTATIVE|IFA_F_OPTIMISTIC)) {
 			if (dad) {
 				if (dev->type == ARPHRD_IEEE802_TR) {
-					unsigned char *sadr = skb->mac.raw;
+					const unsigned char *sadr;
+					sadr = skb_mac_header(skb);
 					if (((sadr[8] ^ dev->dev_addr[0]) & 0x7f) == 0 &&
 					    sadr[9] == dev->dev_addr[1] &&
 					    sadr[10] == dev->dev_addr[2] &&