[NETFILTER]: ipt_ECN/ipt_TOS: fix incorrect checksum update

Even though the tos field is only a single byte large, the values need to
be converted to net-endian for the checkum update so they are in the
corrent byte position. Also fix incorrect endian annotations.

Reported by Stephane Chazelas <Stephane_Chazelas@yahoo.fr>

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>