[PKT_SCHED]: Convert tc action functions to single skb pointers

tcf_action_exec only gets a single skb pointer and doesn't own the skb,
but passes double skb pointers (to a local variable) to the action
functions. Change to use single skb pointers everywhere.

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