xen: netback: handle compound page fragments on transmit.

xen: netback: handle compound page fragments on transmit.

An SKB paged fragment can consist of a compound page with order > 0.
However the netchannel protocol deals only in PAGE_SIZE frames.

Handle this in netbk_gop_frag_copy and xen_netbk_count_skb_slots by
iterating over the frames which make up the page.

Signed-off-by: Ian Campbell <[email protected]>
Cc: Eric Dumazet <[email protected]>
Cc: Konrad Rzeszutek Wilk <[email protected]>
Cc: Sander Eikelenboom <[email protected]>
Tested-by: Konrad Rzeszutek Wilk <[email protected]>
Signed-off-by: David S. Miller <[email protected]>