net: replace __constant_{endian} uses in net headers

Base versions handle constant folding now.  For headers exposed to
userspace, we must only expose the __ prefixed versions.

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/transp_v6.h b/include/net/transp_v6.h
index 876b6f2..bfb240c 100644
--- a/include/net/transp_v6.h
+++ b/include/net/transp_v6.h
@@ -46,7 +46,7 @@
 						  struct ipv6_txoptions *opt,
 						  int *hlimit, int *tclass);
 
-#define		LOOPBACK4_IPV6		__constant_htonl(0x7f000006)
+#define		LOOPBACK4_IPV6		cpu_to_be32(0x7f000006)
 
 /*
  *	address family specific functions