ndisc_router_discovery() failed to add default route

In Ubuntu 14.04 (and probably in other Debian derivatives), network interfaces with a statically configured IPv6 address and gateway will still accept Neighborhood Discovery Protocol Router Advertisements and attempt to process them, leading to log spam of the following form:

...
ICMPv6 RA: ndisc_router_discovery() failed to add default route.
ICMPv6 RA: ndisc_router_discovery() failed to add default route.
ICMPv6 RA: ndisc_router_discovery() failed to add default route.
...

To prevent this, disable acceptance of RAs by adding accept_ra 0 to the static configuration, as follows:

iface eth0 inet6 static
        address <static_ipv6_addr>
        netmask <netmask>
        gateway <gateway_addr>
        accept_ra 0