RDMA/nldev: Return port capability flag for IB only

Port capability flag represents IBTA PortInfo:CapabilityMask,
but was mistakenly mixed with non-relevant fields. Return that
information for IB only.

Link: https://patchwork.kernel.org/patch/10386245/


Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>