Do not generate R3 compat firewall rules if R4 format is supported
Do not generate R3 compat firewall rules if R4 format is supported

R3 format had limitation of ~40 rules per VM. Do not generate compat
rules (possibly hitting that limitation) if new format, free of that
limitation is supported.

Fixes QubesOS/qubes-issues#1570
Fixes QubesOS/qubes-issues#4228

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