selftests/bpf/test_xdp_redirect_multi: use temp netns for testing

selftests/bpf/test_xdp_redirect_multi: use temp netns for testing

BugLink: https://bugs.launchpad.net/bugs/1969110
[ Upstream commit cec74489a8dee93053340ec88ea938ff4008c3c0 ]

Use temp netns instead of hard code name for testing in case the netns
already exists.

Remove the hard code interface index when creating the veth interfaces.
Because when the system loads some virtual interface modules, e.g. tunnels.
the ifindex of 2 will be used and the cmd will fail.

As the netns has not created if checking environment failed. Trap the
clean up function after checking env.

Fixes: 8955c1a32987 ("selftests/bpf/xdp_redirect_multi: Limit the tests in netns")
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Acked-by: William Tu <u9012063@gmail.com>
Link: https://lore.kernel.org/r/20220125081717.1260849-2-liuhangbin@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
(cherry picked from commit c41832e7dadd99c012c3713a5df4dcb801c8be3a)
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>