RDMA/mlx5: Perform check if QP creation flow is valid

Fast check that kernel and user flows provides enough
data to create QP.

Link: https://lore.kernel.org/r/20200427154636.381474-4-leon@kernel.org
Reviewed-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>