[IPVS]: Do not use skb_checksum_help(), create and use nf_reset_debug()

[IPVS]: Do not use skb_checksum_help(), create and use nf_reset_debug()

	Appended is a 2nd version that uses nf_reset_debug.

- do not use skb_checksum_help in input path as ipvs can handle
incoming CHECKSUM_HW packets

- do not use skb_checksum_help in forwarding path

- claim that checksum is valid (CHECKSUM_NONE) when entering output
path for out->in packets

- do not reset/destroy the nfct in IP_VS_XMIT, the intention is to
reset the debugging field just to avoid log floods from nf_debug_ip_*
functions, it is known that the ipvs packets traverse other
hooks, eg. LOCAL_IN->LOCAL_OUT. Use nf_reset_debug instead of nf_reset.

Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: David S. Miller <davem@davemloft.net>