ethtool: Add reset operation

After updating firmware stored in flash, users may wish to reset the
relevant hardware and start the new firmware immediately.  This should
not be completely automatic as it may be disruptive.

A selective reset may also be useful for debugging or diagnostics.

This adds a separate reset operation which takes flags indicating the
components to be reset.  Drivers are allowed to reset only a subset of
those requested, and must indicate the actual subset.  This allows the
use of generic component masks and some future expansion.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>