RDMA/cma: Fix locking for the RDMA_CM_CONNECT state

It is currently a bit confusing, but the design is if the handler_mutex
is held, and the state is in RDMA_CM_CONNECT, then the state cannot leave
RDMA_CM_CONNECT without also serializing with the handler_mutex.

Make this clearer by adding a direct assertion, fixing the usage in
rdma_connect and generally using READ_ONCE to read the state value.

Link: https://lore.kernel.org/r/20200902081122.745412-2-leon@kernel.org


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