sfc: Move details of a Falcon bug workaround out of ethtool.c

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

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

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

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

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

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