[NETLINK]: Restore API compatibility of address and neighbour bits

Restore API compatibility due to bits moved from rtnetlink.h to
separate headers.
Signed-off-by: NThomas Graf <tgraf@suug.ch>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/linux/rtnetlink.h

@@ -3,6 +3,8 @@
 
 #include <linux/netlink.h>
 #include <linux/if_link.h>
+#include <linux/if_addr.h>
+#include <linux/neighbour.h>
 
 /****
  *		Routing/neighbour discovery messages.