netlink: constify nlmsghdr arguments

Consitfy nlmsghdr arguments to a couple of functions as preparation
for the next patch, which will constify the netlink message data in
all nfnetlink users.

Signed-off-by: Patrick McHardy <kaber@trash.net>
diff --git a/include/net/netlink.h b/include/net/netlink.h
index 007bdb0..a63b219 100644
--- a/include/net/netlink.h
+++ b/include/net/netlink.h
@@ -365,7 +365,7 @@
  *
  * See nla_parse()
  */
-static inline int nlmsg_parse(struct nlmsghdr *nlh, int hdrlen,
+static inline int nlmsg_parse(const struct nlmsghdr *nlh, int hdrlen,
 			      struct nlattr *tb[], int maxtype,
 			      const struct nla_policy *policy)
 {
@@ -414,7 +414,7 @@
  *
  * Returns 1 if a report back to the application is requested.
  */
-static inline int nlmsg_report(struct nlmsghdr *nlh)
+static inline int nlmsg_report(const struct nlmsghdr *nlh)
 {
 	return !!(nlh->nlmsg_flags & NLM_F_ECHO);
 }
diff --git a/include/net/rtnetlink.h b/include/net/rtnetlink.h
index 3c1895e..85ba560 100644
--- a/include/net/rtnetlink.h
+++ b/include/net/rtnetlink.h
@@ -14,7 +14,7 @@
 extern int	rtnl_unregister(int protocol, int msgtype);
 extern void	rtnl_unregister_all(int protocol);
 
-static inline int rtnl_msg_family(struct nlmsghdr *nlh)
+static inline int rtnl_msg_family(const struct nlmsghdr *nlh)
 {
 	if (nlmsg_len(nlh) >= sizeof(struct rtgenmsg))
 		return ((struct rtgenmsg *) nlmsg_data(nlh))->rtgen_family;