To get bytes in/out:

# netstat -bI bridge0

For example to get bytes in/out on tap interface:

# netstat -bI tap0
Name    Mtu Network       Address              Ipkts Ierrs Idrop     Ibytes    Opkts Oerrs     Obytes  Coll
tap0*  1500 <Link#7>      00:bd:49:f6:f6:00     1689     0     0     153380        0     0     161697     0