rdma: Add context resource tracking information

rdma: Add context resource tracking information

Sample output:

$ rdma res show ctx
dev ibp8s0f0 ctxn 0 pid 980 comm ibv_rc_pingpong
dev ibp8s0f0 ctxn 1 pid 981 comm ibv_rc_pingpong
dev ibp8s0f0 ctxn 2 pid 992 comm ibv_rc_pingpong
dev ibp8s0f1 ctxn 0 pid 984 comm ibv_rc_pingpong
dev ibp8s0f1 ctxn 1 pid 987 comm ibv_rc_pingpong

$ rdma res show ctx dev ibp8s0f1
dev ibp8s0f1 ctxn 0 pid 984 comm ibv_rc_pingpong
dev ibp8s0f1 ctxn 1 pid 987 comm ibv_rc_pingpong

Reviewed-by: Mark Zhang <markz@mellanox.com>
Reviewed-by: Ido Kalir <idok@nvidia.com>
Signed-off-by: Neta Ostrovsky <netao@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: David Ahern <dsahern@kernel.org>