ethtool: Add ability to flash transceiver modules' firmware

Add the ability to flash the modules' firmware by implementing the
interface between the user space and the kernel.

Example from a succeeding implementation:

 # ethtool --flash-module-firmware swp40 file test.bin

 Transceiver module firmware flashing started for device swp40
 Transceiver module firmware flashing in progress for device swp40
 Progress: 99%
 Transceiver module firmware flashing completed for device swp40

In addition, add infrastructure that allows modules to set socket-specific
private data. This ensures that when a socket is closed from user space
during the flashing process, the right socket halts sending notifications
to user space until the work item is completed.

Signed-off-by: Danielle Ratson <danieller@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>