Merge branch 'mptcp-cleanups'

Matthieu Baerts says:

====================
mptcp: various small cleanups

Patch 1 makes a function static because it is only used in one file.

Patch 2 adds info about the git trees we use to help occasional devs.

Patch 3 removes an unused variable.

Patch 4 removes duplicated entries from the help menu of a tool used in
MPTCP selftests.

Patch 5 removes some ShellCheck warnings in mptcp_join.sh selftest.

Only very minor improvements then.
====================

Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: David S. Miller <davem@davemloft.net>