From: Stephen Hemminger <redacted>
Date: Thu, 28 Sep 2006 16:27:04 -0700

It got added by this:

commit 0844565fb8a9418f5a860aa480c1aef70319c9a2
Author: Thomas Graf [off-list ref]
Date:   Fri Aug 4 23:05:56 2006 -0700

    [NET]: Move netlink interface bits to linux/if.h
    
    Signed-off-by: Thomas Graf [off-list ref]
    Signed-off-by: David S. Miller [off-list ref]

Stephen, we just removed the troublesome bits from linux/if.h when I
put in Yoshifuji's patches last night, it should explicitly remove
this problem.

You will thus see that linux/rtnetlink.h no longer includes
linux/if.h, which is why your errors were completely perplexing
to me.  Instead, it includes linux/if_link.h

It's been in my tree since last night, and if you had used
the rtnetlink.h from my current tree you wouldn't have seen
the error.