Depend on IPv6 stack to resolve link local address for RoCEv2 in ibcore.

RoCEv1 does not use the IPv6 stack to resolve the link local DGID since it
uses GID address. It forms the DMAC directly from the DGID.

Linux commit:
56d0a7d9a0f045ee27a001762deac28c7d28e2e4

MFC after: 1 week
Sponsored by: Mellanox Technologies