RDMA/uverbs: Check CAP_NET_RAW in user namespace for flow create

RDMA/uverbs: Check CAP_NET_RAW in user namespace for flow create

Currently, the capability check is done in the default
init_user_ns user namespace. When a process runs in a
non default user namespace, such check fails. Due to this
when a process is running using Podman, it fails to create
the flow resource.

Since the RDMA device is a resource within a network namespace,
use the network namespace associated with the RDMA device to
determine its owning user namespace.

Fixes: 436f2ad05a0b ("IB/core: Export ib_create/destroy_flow through uverbs")
Signed-off-by: Parav Pandit <parav@nvidia.com>
Suggested-by: Eric W. Biederman <ebiederm@xmission.com>
Link: https://patch.msgid.link/6df6f2f24627874c4f6d041c19dc1f6f29f68f84.1750963874.git.leon@kernel.org
Signed-off-by: Leon Romanovsky <leon@kernel.org>