OVM : MTU downgrade problem

https://oss.oracle.com/pipermail/oraclevm-errata/2015-February/000275.html

[4.3.0-55.el6.1] - Before connecting the emulated network interface (vif.x.y-emu) to a bridge, change the emu MTU to equal the MTU of the bridge to prevent the bridge from downgrading its own MTU to equal the emu MTU.