irq: MSI first, and poll the INTx lines that never arrive

PCI drivers took their interrupt from INTERRUPT_LINE. On real hardware
that is the 8259's number, not the IOAPIC pin the device is wired to
(that is in ACPI _PRT, which needs AML), so nothing ever arrived. xHCI
is entirely interrupt-driven, so the USB keyboard and a USB root would
have hung even on a clean boot. Under QEMU the two numbers agree,
which is why it never showed.

- pci_irq_attach()/pci_irq_detach(): MSI, then MSI-X if the driver
  allows it, then INTx. The handler is registered before MSI is
  enabled, so no edge is lost. xHCI, e1000, r8169 and rtl8139 use it.
- Lines 24-29 are MSI vectors. The LAPIC error vector moves from 19,
  which is a PCI pin on Intel chipsets, to 30. Nothing is placed at or
  above vector 64 (T_SYSCALL).
- A storming line is masked and its handlers are polled instead of
  being left to eat the CPU. A level line that has had a handler for 2 s
  and never fired is polled every tick by a kernel thread.

Tested in QEMU q35 with the root on a USB stick: xHCI and e1000e on
MSI; then MSI disabled and INTx deliberately misrouted, where xHCI got
zero interrupts and the root still mounted through the poller. i440fx
INTx and the rtl8139 hand-over are unchanged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HH7xukt4aaiGj1nQEAoQf1

kernel/drivers/net/rtl8139/rtl8139.c

@@ -360,8 +360,7 @@ rtl8139_probe(struct pci_dev *d)
   wr16(r, R_IMR, ISR_ROK | ISR_RER | ISR_TOK | ISR_TER |
                  ISR_RXOVW | ISR_FOVW | ISR_LINKCHG);
 
-  if (d->irq != 0xFF && d->irq < 24)
-    irq_register(d->irq, rtl8139_intr, r, "rtl8139", 1);
+  pci_irq_attach(d, rtl8139_intr, r, "rtl8139", 0);   // no MSI on this part
 
   r->ready = 1;
   kinfo("rtl8139: %x:%x:%x:%x:%x:%x, %s, irq %d\n",
@@ -405,8 +404,7 @@ rtl8139_release(struct pci_dev *d)
   wr8(r, R_CR, 0);                // receiver and transmitter off
   release(&r->lock);
 
-  if (d->irq != 0xFF && d->irq < 24)
-    irq_unregister(d->irq, rtl8139_intr, r);
+  pci_irq_detach(d, rtl8139_intr, r);
 
   // Reset, and wait for it, so the chip has truly stopped before its buffers
   // are reused. The reset bit clears itself when the chip is done.