Because wait_event() loops are safe vs spurious wakeups we can allow the
occasional sleep -- which ends up being very similar.
Reported-by: Dave Jones <davej@codemonkey.org.uk> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Tested-by: Dave Jones <davej@codemonkey.org.uk> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>