[NETLINK]: add nla_for_each_nested() to the interface list

At the top of include/net/netlink.h is a list of Netlink interfaces, however,
the nla_for_each_nested() macro was not listed.  This patch adds this interface
to the list at the top of the header file.

Signed-off-by: Paul Moore <paul.moore@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/netlink.h b/include/net/netlink.h
index 11dc2e7..2897a73 100644
--- a/include/net/netlink.h
+++ b/include/net/netlink.h
@@ -151,6 +151,7 @@
  *   nla_parse()			parse and validate stream of attrs
  *   nla_parse_nested()			parse nested attribuets
  *   nla_for_each_attr()		loop over all attributes
+ *   nla_for_each_nested()		loop over the nested attributes
  *=========================================================================
  */