net: Provide MemReentrancyGuard * to qemu_new_nic()

net: Provide MemReentrancyGuard * to qemu_new_nic()

Recently MemReentrancyGuard was added to DeviceState to record that the
device is engaging in I/O. The network device backend needs to update it
when delivering a packet to a device.

In preparation for such a change, add MemReentrancyGuard * as a
parameter of qemu_new_nic().

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Reviewed-by: Alexander Bulekov <alxndr@bu.edu>
Signed-off-by: Jason Wang <jasowang@redhat.com>