selftests: mptcp: set addr id for removing testcases

The removing testcases can only delete the addresses from id 1, this
patch added the support for deleting the addresses from any id that user
set.

Signed-off-by: Geliang Tang <geliangtang@gmail.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>