selftests: mptcp: remove duplicated entries in usage

mptcp_connect tool was printing some duplicated entries when showing how
to use it: -j -l -r

While at it, I also:

 - moved the very few entries that were not sorted,

 - added -R that was missing since
   commit 8a4b910d ("mptcp: selftests: add rcvbuf set option"),

 - removed the -u parameter that has been removed in
   commit f730b65c ("selftests: mptcp: try to set mptcp ulp mode in different sk states").

No need to backport this, it is just an internal tool used by our
selftests. The help menu is mainly useful for MPTCP kernel devs.

Acked-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: David S. Miller <davem@davemloft.net>