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/ip6_gre.c b/net/ipv6/ip6_gre.c
index 67e014d..f61f7ad 100644
--- a/net/ipv6/ip6_gre.c
+++ b/net/ipv6/ip6_gre.c
@@ -1622,8 +1622,8 @@
 	    nla_put_be16(skb, IFLA_GRE_OFLAGS, p->o_flags) ||
 	    nla_put_be32(skb, IFLA_GRE_IKEY, p->i_key) ||
 	    nla_put_be32(skb, IFLA_GRE_OKEY, p->o_key) ||
-	    nla_put(skb, IFLA_GRE_LOCAL, sizeof(struct in6_addr), &p->laddr) ||
-	    nla_put(skb, IFLA_GRE_REMOTE, sizeof(struct in6_addr), &p->raddr) ||
+	    nla_put_in6_addr(skb, IFLA_GRE_LOCAL, &p->laddr) ||
+	    nla_put_in6_addr(skb, IFLA_GRE_REMOTE, &p->raddr) ||
 	    nla_put_u8(skb, IFLA_GRE_TTL, p->hop_limit) ||
 	    /*nla_put_u8(skb, IFLA_GRE_TOS, t->priority) ||*/
 	    nla_put_u8(skb, IFLA_GRE_ENCAP_LIMIT, p->encap_limit) ||