Based on some digital archaeology performed by jtomko, it's been determined
that the persistentAddrs variable is no longer necessary...

The variable was added by:
commit 141dea6b
CommitDate: 2010-02-12 17:25:52 +0000
    Add persistence of PCI addresses to QEMU

Where it was set to 0 on domain startup if qemu did not support the
QEMUD_CMD_FLAG_DEVICE capability, to clear the addresses at shutdown,
because QEMU might make up different ones next time.

As of commit f5dd58a6
CommitDate: 2012-07-11 11:19:05 +0200
    qemu: Extended qemuDomainAssignAddresses to be callable from
    everywhere.

this was broken, when the persistentAddrs = 0 assignment was moved
inside qemuDomainAssignPCIAddresses and while it pretends to check
for !QEMU_CAPS_DEVICE, its parent qemuDomainAssignAddresses is only
called if QEMU_CAPS_DEVICE is present.