selftests: mptcp: add testcases for setting the address ID

Since the address ID can be set from user-space, some of the tests in
pm_netlink.sh will fail. This patch fixed the failures, and add the
testcases for setting the address ID.

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>