KVM: Fix unintended qemu-level bridging of nics

Each nic should be connected to its own qemu vlan, to avoid them all
bridging together.

Signed-off-by: Timothy Kuhlman <timkuhlman@gmail.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>
Signed-off-by: Guido Trotter <ultrotter@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>