sfc: Copy RX prefix into skb head area in efx_rx_mk_skb()

We can potentially pull the entire packet contents into the head area
and then free the page it was in.  In order to read an inline
timestamp safely, we need to copy the prefix into the head area as
well.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>

diff --cc drivers/net/ethernet/sfc/net_driver.h
Simple merge

diff --cc drivers/net/ethernet/sfc/rx.c
Simple merge