Source http://www.server-world.info/en/note?os=Fedora_21&p=kvm

UUID=e23ff639-8f6e-4bbe-be1a-c1787467690b
DNS1=127.0.0.1
BOOTPROTO=none
DEVICE=eth0
ONBOOT=yes
IPV6INIT=yes
TYPE=Ethernet
IPADDR=xx.xxx.xxx.142
PREFIX=24
GATEWAY=xxx.xxx.xxx.1
DEFROUTE=yes
IPV4_FAILURE_FATAL=no
IPV6_AUTOCONF=yes
IPV6_DEFROUTE=yes
IPV6_PEERDNS=yes
IPV6_PEERROUTES=yes
IPV6_FAILURE_FATAL=no
NAME="System eth0"

nmcli c add type bridge autoconnect yes con-name br0 ifname br0
nmcli c modify br0 bridge.stp no
nmcli c modify br0 ipv4.addresses "xxx.xxx.xxx.xxx/24 xxx.xxx.xxx.1" ipv4.method manual
nmcli c modify br0 ipv4.dns 127.0.0.1
nmcli c delete eth0
nmcli c add type bridge-slave autoconnect yes con-name eth0 ifname eth0 master br0
systemctl stop NetworkManager; systemctl start NetworkManager