selftests/net: convert netns-name.sh to run it in unique namespace

This test will move the device to netns 1. Add a new test_ns to do this.
Here is the test result after conversion.

# ./netns-name.sh
netns-name.sh [ OK ]

Acked-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

selftests: net: add very basic test for netdev names and namespaces

Add selftest for fixes around naming netdevs and namespaces.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>