ospf6d: Rename ospf6_is_router_abr to more accurately reflect what it does

ospf6d: Rename ospf6_is_router_abr to more accurately reflect what it does

The ospf6_is_router_abr is checking to see if ospfv3 is an abr router
and also setting values.  Let's rename it too `ospf6_check_and_set_router_abr`
to more accurately reflect what it is doing.

Additionally fix coverity #1505176 where we were not checking the return
value of ospf6_is_router_abr like we did every other time.  In this
case we don't care about the return value so indicate that we do not.

Signed-off-by: Donald Sharp <sharpd@nvidia.com>