port_cap_flags2 represents IBTA PortInfo:CapabilityMask2.

The field safely extends the RDMA_NLDEV_ATTR_CAP_FLAGS operand as it was
exported as 64 bit to allow this kind of extension.
Signed-off-by: Michael Guralnik <michaelgur@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>