arm without devices = leaves no PCI function adoptable; takeover also waits ~3 s per missing NIC #2

What happens

With a kmorph.conf that has no devices = key, a takeover adopts no PCI function at all.
kmorphd's network restore then waits about 3 s for every recorded NIC that never appears, so
the takeover takes 6.8 s instead of 0.9 s in my setup. The README lists devices as optional.

Setup

• multikernel/linux 57fd249 (7.0.0-mk4), kmorph 9ec046e (= current main), x86_64, GCC 16.2.1
• QEMU 11.1.3, q35, KVM, 4 vCPUs, 4 GiB; two NICs behind PCIe root ports
  (virtio-net at 0000:01:00.0, e1000e at 0000:02:00.0)
• cpus = 1, memory = 128MB, console = ttyS0, cmdline = earlyprintk=serial,ttyS0,115200 keep_bootcon printk.devkmsg=on
• predecessor crashed with echo c > /proc/sysrq-trigger

Without devices = (7 runs; panic to TAKEN_OVER 6.76 to 6.90 s)

Overlay tx2: +device 0000:00:1f.2 driver=none -> successor
Failed to move device 0000:00:1f.2: -1
kmorphd: error: device 0000:00:1f.2 not adopted (tx 2): Input/output error
... same for 0000:00:1f.3, 0000:01:00.0, 0000:02:00.0
kmorphd: adopted 0 devices: 0 reset, 0 quiesced
kmorphd: warning: network: no interface on 0000:01:00.0 for eth0: Connection timed out
kmorphd: warning: network: no interface on 0000:02:00.0 for eth1: Connection timed out

With devices = 0000:01:00.0 (20 runs in two sessions; panic to TAKEN_OVER 0.84 to 1.03 s)

mk_pcifront: Host fenced: config space is reached directly through ECAM
mk_pcifront: Root bus 0000:00 from /pci@0,0
mk_pcifront: Root bus 0000:02 from /pci@0,2
e1000e 0000:02:00.0 eth1: (PCI Express:2.5GT/s:Width x1) 52:54:00:12:34:57
kmorphd: adopted 3 devices: 1 reset, 2 quiesced
kmorphd: network: eth1 on 0000:02:00.0 restored with 0 addresses and 0 routes

Why (from reading the kernel, not from a debugger)

mk_pcifront_host_fenced() returns early when the successor has no PCI bus
(kernel/multikernel/pcifront.c:150-153), so mk_pcifront_direct_access stays false and
mk_pcifront_adopt_function() returns -EPERM (:704). A successor only has PCI buses for devices
it owns from boot.

Suggestions (none tested)

• Warn in kmorph arm when devices names no PCI device, or say in the README and
  kmorph.conf.example that it is needed for PCI adoption.
• Skip the 3 s wait in the network restore for functions whose adoption just failed.

Not checked: real hardware.