RSC will flush its descriptors every time the interrupt throttle timer
expires.  In addition there are known issues with RSC when the rx-usecs
value is set too low.  As such we are forced to clear the RSC_ENABLED bit
and reset the adapter when the rx-usecs value is set too low.

However we do not need to clear the NETIF_F_LRO flag because it is used to
indicate that the user wants to leave the LRO feature enabled, and in fact
with this change we will now re-enable RSC as soon as the rx-usecs value is
increased and the flag is still set.
Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Ross Brattain <ross.b.brattain@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>