Fix warning on OpenBSD

/src/qemu/net.c: In function `net_check_clients':
/src/qemu/net.c:1287: warning: `has_nic' might be used uninitialized in this function
/src/qemu/net.c:1287: warning: `has_host_dev' might be used uninitialized in this function

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
