selftests:mptcp: fix failure due to whitespace damage

'pm_nl_ctl' was adding a trailing whitespace after having printed the
IP. But at the end, the IP element is currently always the last one.

The bash script launching 'pm_nl_ctl' had trailing whitespaces in the
expected result on purpose. But these whitespaces have been removed when
the patch has been applied upstream. To avoid trailing whitespaces in
the bash code, 'pm_nl_ctl' and expected results have now been adapted.

The MPTCP PM selftest can now pass again.

Fixes: eedbc685

 (selftests: add PM netlink functional tests)
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: David S. Miller <davem@davemloft.net>