sfc: Change entity reset on MC reboot to a new datapath-only reset.

Currently we do an entity reset when we detect an MC reboot.
This messes up SRIOV because it leaves VFs orphaned. The extra
reset is rather redundant anyway, since the MC reboot will have
basically reset everything.

This change replaces the entity reset after MC reboot with a
simpler datapath reset that reallocates resources but doesn't
perform the entity reset.

Signed-off-by: Shradha Shah <sshah@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>