If an RX interrupt was already received but NAPI has not yet run when
the RX timeout happens, we end up in cp_tx_timeout() with RX interrupts
already disabled. Blindly re-enabling them will cause an IRQ storm.

(This is made particularly horrid by the fact that cp_interrupt() always
returns that it's handled the interrupt, even when it hasn't actually
done anything. If it didn't do that, the core IRQ code would have
detected the storm and handled it, I'd have had a clear smoking gun
backtrace instead of just a spontaneously resetting router, and I'd have
at *least* two days of my life back. Changing the return value of
cp_interrupt() will be argued about under separate cover.)

Unconditionally leave RX interrupts disabled after the reset, and
schedule NAPI to check the receive ring and re-enable them.
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>