[IPV6]: Fix ECN bug on big-endian
__constant_htons(2<<4) is not a replacement for
htonl(2<<20).
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>
authored by Al Viro and committed by David S. Miller 95026cd2 02e60370