lguest: allow any process to send interrupts

We currently only allow the Launcher process to send interrupts, but it
as we already send interrupts from the hrtimer, it's a simple matter of
extracting that code into a common set_interrupt routine.

As we switch to a thread per virtqueue, this avoids a bottleneck through the
main Launcher process.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/drivers/lguest/lg.h b/drivers/lguest/lg.h
index 6201ce5..040cb70 100644
--- a/drivers/lguest/lg.h
+++ b/drivers/lguest/lg.h
@@ -143,6 +143,7 @@
 /* interrupts_and_traps.c: */
 unsigned int interrupt_pending(struct lg_cpu *cpu, bool *more);
 void try_deliver_interrupt(struct lg_cpu *cpu, unsigned int irq, bool more);
+void set_interrupt(struct lg_cpu *cpu, unsigned int irq);
 bool deliver_trap(struct lg_cpu *cpu, unsigned int num);
 void load_guest_idt_entry(struct lg_cpu *cpu, unsigned int i,
 			  u32 low, u32 hi);