netlink: implement nla_put_in_addr and nla_put_in6_addr

IP addresses are often stored in netlink attributes. Add generic functions
to do that.

For nla_put_in_addr, it would be nicer to pass struct in_addr but this is
not used universally throughout the kernel, in way too many places __be32 is
used to store IPv4 address.

Signed-off-by: Jiri Benc <jbenc@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/addrlabel.c b/net/ipv6/addrlabel.c
index 3cc50e2..882124e 100644
--- a/net/ipv6/addrlabel.c
+++ b/net/ipv6/addrlabel.c
@@ -477,7 +477,7 @@
 
 	ip6addrlbl_putmsg(nlh, p->prefixlen, p->ifindex, lseq);
 
-	if (nla_put(skb, IFAL_ADDRESS, 16, &p->prefix) < 0 ||
+	if (nla_put_in6_addr(skb, IFAL_ADDRESS, &p->prefix) < 0 ||
 	    nla_put_u32(skb, IFAL_LABEL, p->label) < 0) {
 		nlmsg_cancel(skb, nlh);
 		return -EMSGSIZE;