This info has been added a while ago in the kernel [1], but it was not
displayed in 'ip monitor'.

Now, 'server_side' is displayed if the attribute is defined and set to
true. It looks better to do that instead of showing server_side=0. Note
that since v6.18 [2], this attribute is only defined if it is set to
true.

Link: https://git.kernel.org/torvalds/c/41b3c69bf941 [1]
Link: https://git.kernel.org/torvalds/c/c9809f03c158 [2]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 ip/ipmptcp.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/ip/ipmptcp.c b/ip/ipmptcp.c
index 2908b69e..aaacc0a5 100644
--- a/ip/ipmptcp.c
+++ b/ip/ipmptcp.c
@@ -536,6 +536,8 @@ static int mptcp_monitor_msg(struct rtnl_ctrl_data *ctrl,
 		printf(" reset_reason=%u", rta_getattr_u32(tb[MPTCP_ATTR_RESET_REASON]));
 	if (tb[MPTCP_ATTR_RESET_FLAGS])
 		printf(" reset_flags=0x%x", rta_getattr_u32(tb[MPTCP_ATTR_RESET_FLAGS]));
+	if (tb[MPTCP_ATTR_SERVER_SIDE] && rta_getattr_u8(tb[MPTCP_ATTR_SERVER_SIDE]))
+		printf(" server_side");
 
 	puts("");
 out:

-- 
2.51.0