selftests: mptcp: add ADD_ADDR timeout test case

This patch added the test case for retransmitting ADD_ADDR when timeout
occurs. It set NS1's add_addr_timeout to 1 second, and drop NS2's ADD_ADDR
echo packets.

Here we need to slow down the transfer process of all data to let the
ADD_ADDR suboptions can be retransmitted three times. So we added a new
parameter "speed" for do_transfer, it can be set with fast or slow.

We also added three new optional parameters for run_tests, and dropped
run_remove_tests function.

Since we added the netfilter rules in this test case, we need to update
the "config" file.

Suggested-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Suggested-by: Paolo Abeni <pabeni@redhat.com>
Acked-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Geliang Tang <geliangtang@gmail.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>