selftests: mptcp: add token for get_addr

The command get_addr() of pm_nl_ctl can be used like this in in-kernel PM:

	pm_nl_ctl get $id

This patch adds token argument for it to support userspace PM:

	pm_nl_ctl get $id token $token

If 'token $token' is passed to get_addr(), copy it into the kernel netlink.

Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>