Firstoff, adjust the /etc/network/interfaces file to look like this:

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# device: eth0
auto eth0
iface eth0 inet static
        address         78.46.37.118
        netmask         255.255.255.255
        gateway         78.46.37.97
        pointopoint     78.46.37.97

iface eth0 inet6 static
        address         2a01:4f8:110:3148::2
        netmask         64
        gateway         fe80::1

auto vmbr0
iface vmbr0 inet static
        address         78.46.37.118
        netmask         255.255.255.255
        bridge_ports    none
        bridge_stp      off
        bridge_fd       0
        post-up         ip route add 78.46.37.108/32 dev vmbr0
        post-up         ip route add 78.46.37.110/32 dev vmbr0
        post-up         ip route add 78.46.37.114/32 dev vmbr0

iface vmbr0 inet6 static
        address         2a01:4f8:110:3148::2
        netmask         64
        post-up         ip -6 neigh add proxy 2a01:4f8:110:3148::3 dev eth0
        post-up         ip -6 neigh add proxy 2a01:4f8:110:3148::4 dev eth0
        post-up         ip -6 neigh add proxy 2a01:4f8:110:3148::5 dev eth0
        post-up         ip -6 neigh add proxy 2a01:4f8:110:3148::6 dev eth0
        post-up         ip -6 neigh add proxy 2a01:4f8:110:3148::7 dev eth0
        post-up         ip -6 neigh add proxy 2a01:4f8:110:3148::8 dev eth0
        post-up         ip -6 neigh add proxy 2a01:4f8:110:3148::9 dev eth0

Secondly, adjust you KVM guest network config to look like this (similar, you might want to replace the MAC address of the guest):

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    <interface type='bridge'>
      <mac address='52:54:00:3c:de:d1'/>
      <source bridge='vmbr0'/>
      <model type='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    </interface>