I experienced this same issue. I hope it gets resolved soon. Another workaround is to copy /usr/libexec/qemu/qemu-bridge-helper back to /usr/lib/qemu/qemu-bridge-helper.
I tried Michael Ott's suggestion. I edited /etc/apparmor.d/usr.sbin.libvirtd to reference /usr/libexec/qemu/qemu-bridge-helper, and I re-parsed the AppArmor profile. However, that wasn't sufficient on its own. I needed to set bridge_helper = "/usr/libexec/qemu/qemu-bridge-helper" in qemu.conf. I'm doing this for a qemu/kvm user session, so I did this in ~/.config/libvirt/qemu.conf.
