selftests: hsr: Fix "File exists" errors for hsr_ping

The hsr_ping test reports the following errors:

 INFO: preparing interfaces for HSRv0.
 INFO: Initial validation ping.
 INFO: Longer ping test.
 INFO: Cutting one link.
 INFO: Delay the link and drop a few packages.
 INFO: All good.
 INFO: preparing interfaces for HSRv1.
 RTNETLINK answers: File exists
 RTNETLINK answers: File exists
 RTNETLINK answers: File exists
 RTNETLINK answers: File exists
 RTNETLINK answers: File exists
 RTNETLINK answers: File exists
 Error: ipv4: Address already assigned.
 Error: ipv6: address already assigned.
 Error: ipv4: Address already assigned.
 Error: ipv6: address already assigned.
 Error: ipv4: Address already assigned.
 Error: ipv6: address already assigned.
 INFO: Initial validation ping.

That is because the cleanup code for the 2nd round test before
"setup_hsr_interfaces 1" is removed incorrectly in commit 680fda4f
("test: hsr: Remove script code already implemented in lib.sh").

This patch fixes it by re-setup the namespaces using

	setup_ns ns1 ns2 ns3

command before "setup_hsr_interfaces 1". It deletes previous namespaces
and create new ones.

Fixes: 680fda4f

 ("test: hsr: Remove script code already implemented in lib.sh")
Reviewed-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
Link: https://lore.kernel.org/r/6485d3005f467758d49f0f313c8c009759ba6b05.1716374462.git.tanggeliang@kylinos.cn
Signed-off-by: Paolo Abeni <pabeni@redhat.com>