ipv6: constify dev_addr passing

In preparation for netdev->dev_addr being constant
make all relevant arguments in ndisc constant.
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/ndisc.h

@@ -137,7 +137,7 @@ struct ndisc_options *ndisc_parse_options(const struct net_device *dev,
 					  u8 *opt, int opt_len,
 					  struct ndisc_options *ndopts);
 
-void __ndisc_fill_addr_option(struct sk_buff *skb, int type, void *data,
+void __ndisc_fill_addr_option(struct sk_buff *skb, int type, const void *data,
 			      int data_len, int pad);
 
 #define NDISC_OPS_REDIRECT_DATA_SPACE	2

net/ipv6/addrconf.c

@@ -2237,12 +2237,12 @@ static int addrconf_ifid_6lowpan(u8 *eui, struct net_device *dev)
 
 static int addrconf_ifid_ieee1394(u8 *eui, struct net_device *dev)
 {
-	union fwnet_hwaddr *ha;
+	const union fwnet_hwaddr *ha;
 
 	if (dev->addr_len != FWNET_ALEN)
 		return -1;
 
-	ha = (union fwnet_hwaddr *)dev->dev_addr;
+	ha = (const union fwnet_hwaddr *)dev->dev_addr;
 
 	memcpy(eui, &ha->uc.uniq_id, sizeof(ha->uc.uniq_id));
 	eui[0] ^= 2;

net/ipv6/ndisc.c

@@ -142,7 +142,7 @@ struct neigh_table nd_tbl = {
 };
 EXPORT_SYMBOL_GPL(nd_tbl);
 
-void __ndisc_fill_addr_option(struct sk_buff *skb, int type, void *data,
+void __ndisc_fill_addr_option(struct sk_buff *skb, int type, const void *data,
 			      int data_len, int pad)
 {
 	int space = __ndisc_opt_addr_space(data_len, pad);
@@ -165,7 +165,7 @@ void __ndisc_fill_addr_option(struct sk_buff *skb, int type, void *data,
 EXPORT_SYMBOL_GPL(__ndisc_fill_addr_option);
 
 static inline void ndisc_fill_addr_option(struct sk_buff *skb, int type,
-					  void *data, u8 icmp6_type)
+					  const void *data, u8 icmp6_type)
 {
 	__ndisc_fill_addr_option(skb, type, data, skb->dev->addr_len,
 				 ndisc_addr_option_pad(skb->dev->type));