if your NIC ( eth0) of the KVM (VM) is on the host device br0,and you want to see all the network traffics,
what you can do is:
on the hosting machine
brctl setageing <bridgename> 0
this will turn the bridge like a HUB
The reason is: setting the ageing of the bridge to 0 , so it basically never has a list of learnt MAC addresses , thus forcing it to transmit the packets regardless of whether the destination is connected via that port or not.
References:
http://adamdoupe.com/blog/2010/10/22/configuring-linux-bridge-to-act-as-a-hub/