ospf6d: fix duplicated packet read

ospf6d: fix duplicated packet read

When OSPFv3 router is configured in both default and non-default VRFs,
every packet destined to a non-default VRF is read twice. This makes it
impossible to establish neighborship because every DbDesc packet is
treated as duplicated and we end up infinitely exchanging DbDescs.

We should drop packets received in the default VRF if an interface we
received it on is bound to another VRF.

Same thing was done for OSPFv2 in 555691e.

Signed-off-by: Igor Ryzhov <iryzhov@nfware.com>