[NET] napi: use non-interruptible sleep in napi_disable

The current napi_disable() uses msleep_interruptible() but doesn't
(and can't) exit in case there's a signal, thus ending up doing a
hot spin without a cpu_relax. Use uninterruptible sleep instead.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Jeff Garzik <jeff@garzik.org>
Signed-off-by: David S. Miller <davem@davemloft.net>