selftests: mlxsw: spectrum-2: Add IPv6 variant of simple delta rehash test

Track the basic codepaths of delta rehash handling,
using mlxsw tracepoints. Use IPv6 addresses.

Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>