[SK_BUFF]: Use skb_reset_network_header after skb_push

Some more cases where skb->nh.iph was being set that were converted
to using skb_reset_network_header.

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