pskb_copy — create copy of an sk_buff with private head.
struct sk_buff * pskb_copy (struct sk_buff * skb, gfp_t gfp_mask);
Make a copy of both an &sk_buff and part of its data, located
in header. Fragmented data remain shared. This is used when
the caller wishes to modify only header of &sk_buff and needs
private copy of the header to alter. Returns NULL on failure
or the pointer to the buffer on success.
The returned buffer has a reference count of 1.