mptcp: add missing documented NL params

'loc_id' and 'rem_id' are set in all events linked to subflows but those
were missing in the events description in the comments.

Fixes: b911c97c

 ("mptcp: add netlink event support")
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>