vm/qemu: allow to specify network device type
vm/qemu: allow to specify network device type

Switch to the new qemu format for setting up network for all arches.
Add "network_device" configuration parameter to specify the network device type.

For some architectures we did not have a network device type specified before,
some default was used, but it's unclear what it was. Use virtio-net-pci
for these arches as newer/faster thing, e1000 is Intel so probably wasn't
used/supported for non-Intel arches.

google/syzkaller,xairy/syzkaller,xairy/syzkaller,xairy/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,xairy/syzkaller,google/syzkaller,google/syzkaller,google/syzkaller,google/syzkaller