RDMA/nldev: Return "-EAGAIN" if the cm_id isn't from expected port

When filling a cm_id entry, return "-EAGAIN" instead of 0 if the cm_id
doesn'the have the same port as requested, otherwise an incomplete entry
may be returned, which causes "rdam res show cm_id" to return an error.

For example on a machine with two rdma devices with "rping -C 1 -v -s"
running background, the "rdma" command fails:
  $ rdma -V
  rdma utility, iproute2-5.19.0
  $ rdma res show cm_id
  link mlx5_0/- cm-idn 0 state LISTEN ps TCP pid 28056 comm rping src-addr 0.0.0.0:7174
  error: Protocol not available

While with this fix it succeeds:
  $ rdma res show cm_id
  link mlx5_0/- cm-idn 0 state LISTEN ps TCP pid 26395 comm rping src-addr 0.0.0.0:7174
  link mlx5_1/- cm-idn 0 state LISTEN ps TCP pid 26395 comm rping src-addr 0.0.0.0:7174

Fixes: 00313983 ("RDMA/nldev: provide detailed CM_ID information")
Signed-off-by: Mark Zhang <markzhang@nvidia.com>
Link: https://lore.kernel.org/r/a08e898cdac5e28428eb749a99d9d981571b8ea7.1667810736.git.leonro@nvidia.comSigned-off-by: Leon Romanovsky <leon@kernel.org>

drivers/infiniband/core/nldev.c

@@ -552,7 +552,7 @@ static int fill_res_cm_id_entry(struct sk_buff *msg, bool has_cap_net_admin,
 	struct rdma_cm_id *cm_id = &id_priv->id;
 
 	if (port && port != cm_id->port_num)
-		return 0;
+		return -EAGAIN;
 
 	if (cm_id->port_num &&
 	    nla_put_u32(msg, RDMA_NLDEV_ATTR_PORT_INDEX, cm_id->port_num))