RDMA/uverbs: Fix validity check for modify QP

Uverbs shouldn't enforce QP state in the command unless the user set the QP
state bit in the attribute mask.

In addition, only copy qp attr fields which have the corresponding bit set
in the attribute mask over to the internal attr structure.

Fixes: 88de869b ("RDMA/uverbs: Ensure validity of current QP state value")
Fixes: bc38a6ab ("[PATCH] IB uverbs: core implementation")
Signed-off-by: Majd Dibbiny <majd@mellanox.com>
Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>