IB/core: Allow vlan link local address based RoCE GIDs

IPv6 link local address for a VLAN netdevice has nothing to do with its
resemblance with the default GID, because VLAN link local GID is in
different layer 2 domain.

Now that RoCE MAD packet processing and route resolution consider the
right GID index, there is no need for an unnecessary check which prevents
the addition of vlan based IPv6 link local GIDs.

Signed-off-by: Parav Pandit <parav@mellanox.com>
Reviewed-by: Daniel Jurgens <danielj@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>