selftests: icmp_redirect: support expected failures

selftests: icmp_redirect: support expected failures

BugLink: https://bugs.launchpad.net/bugs/1880645
According to a comment in commit 99513cfa16c6 ("selftest: Fixes for
icmp_redirect test") the test "IPv6: mtu exception plus redirect" is
expected to fail, because of a bug in the IPv6 logic that hasn't been
fixed yet apparently.

We should probably consider this failure as an "expected failure",
therefore change the script to return XFAIL for that particular test and
also report the total amount of expected failures at the end of the run.

Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 0a36a75c6818800c67057458376e99b5f77c2a1f)
Signed-off-by: Po-Hsu Lin <po-hsu.lin@canonical.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>