Add a method for query port under the uverbs global methods.  Current
ib_port_attr struct is passed as a single attribute and port_cap_flags2 is
added as a new attribute to the function.
Signed-off-by: Michael Guralnik <michaelgur@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>