vm/mix/net: fill QubesDB for already connected VMs
vm/mix/net: fill QubesDB for already connected VMs

There may be cases when VM providing the network to other VMs is started
later - for example VM restart. While this is rare case (and currently
broken because of QubesOS/qubes-issues#1426), do not assume it will
always be the case.

QubesOS/qubes-core-admin,QubesOS/qubes-core-admin,marmarek/qubes-core-admin,QubesOS/qubes-core-admin,marmarek/qubes-core-admin,marmarek/qubes-core-admin