[SK_BUFF] ipv6: More skb_reset_network_header conversions related to skb_pull

Now related to this form:

skb->nh.ipv6h = (struct ipv6hdr *)skb_put(skb, length);

That, as the others, is done when skb->tail is still equal to skb->data, making
the conversion to skb_reset_network_header possible.

Also one more case equivalent to skb->nh.raw = skb->data, of this form:

iph = (struct ipv6hdr *)skb->data;
<SNIP>
skb->nh.ipv6h = iph;

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>