qlge: remove open-coded skb_cow_head.

Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Cc: Jitendra Kalsaria <jitendra.kalsaria@qlogic.com>
Cc: Shahed Shaikh <shahed.shaikh@qlogic.com>
Cc: Ron Mercer <ron.mercer@qlogic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>