net: dsa: Remove dangerous DSA_SKB_CLONE() macro

This does not cause any bug now because it has no users, but its body
contains two pointer definitions within a code block:

		struct sk_buff *clone = _clone;	\
		struct sk_buff *skb = _skb;	\

When calling the macro as DSA_SKB_CLONE(clone, skb), these variables
would obscure the arguments that the macro was called with, and the
initializers would be a no-op instead of doing their job (undefined
behavior, by the way, but GCC nicely puts NULL pointers instead).

So simply remove this broken macro and leave users to simply call
"DSA_SKB_CB(skb)->clone = clone" by hand when needed.

There is one functional difference when doing what I just suggested
above: the control block won't be transferred from the original skb into
the clone. Since there's no foreseen need for the control block in the
clone ATM, this is ok.

Fixes: b68b0dd0 ("net: dsa: Keep private info in the skb->cb")
Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>