RDMA/nldev: Expose whether RDMA monitoring is supported

Extend the "rdma sys" command to display whether RDMA
monitoring is supported.

RDMA monitoring is not supported in mlx4 because it does
not use the ib_device_set_netdev() API, which sends the
RDMA events.

Example output for kernel where monitoring is supported:
$ rdma sys show
netns shared privileged-qkey off monitor on copy-on-fork on

Example output for kernel where monitoring is not supported:
$ rdma sys show
netns shared privileged-qkey off monitor off copy-on-fork on
Signed-off-by: Chiara Meiohas <cmeiohas@nvidia.com>
Signed-off-by: Michael Guralnik <michaelgur@nvidia.com>
Link: https://patch.msgid.link/20240909173025.30422-8-michaelgur@nvidia.comSigned-off-by: Leon Romanovsky <leon@kernel.org>

drivers/infiniband/core/nldev.c

@@ -1952,6 +1952,12 @@ static int nldev_sys_get_doit(struct sk_buff *skb, struct nlmsghdr *nlh,
 		nlmsg_free(msg);
 		return err;
 	}
+
+	err = nla_put_u8(msg, RDMA_NLDEV_SYS_ATTR_MONITOR_MODE, 1);
+	if (err) {
+		nlmsg_free(msg);
+		return err;
+	}
 	/*
 	 * Copy-on-fork is supported.
 	 * See commits:

include/uapi/rdma/rdma_netlink.h

@@ -579,6 +579,7 @@ enum rdma_nldev_attr {
 
 	RDMA_NLDEV_ATTR_EVENT_TYPE,		/* u8 */
 
+	RDMA_NLDEV_SYS_ATTR_MONITOR_MODE,	/* u8 */
 	/*
 	 * Always the end
 	 */