Having both default_netvm and default_fw_netvm cause a lot of confusion,
because it isn't clear for the user which one is used when. Additionally
changing provides_network property may also change netvm property, which
may be unintended effect. This as a whole make it hard to:
- cover all netvm-changing actions with policy for Admin API
- cover all netvm-changing events (for example to apply the change to
the running VM, or to check for netvm loops)
As suggested by @qubesuser, kill the default_fw_netvm property and
simplify the logic around it.
Since we're past rc1, implement also migration logic. And add tests for
said migration.
FixesQubesOS/qubes-issues#3247
f223594f92