Start qubes-firewall (which will add "DROP by default" rule) before
enabling IP forwarding, to not leave a time slot where some connection
could go around configured firewall.
QubesOS/qubes-issues#3269
Get rid of underscores in filenames, use dashes instead.
This is first part of cleanup in filenames.
"qubes_rpc" still untouched - will be in separate commit.