perftune.py: Fix the dump options after adding multiple nics option
perftune.py: Fix the dump options after adding multiple nics option

The "dump_config()" function got broken by commit
a2fc9d72c31b97840bc75ae49dbd6f4b6d394e25 ("perftune.py: support passing
multiple --nic options to tune multiple interfaces at once").

Refs: https://github.com/scylladb/scylla/issues/7895
Reviewed-by: Amos Kong <eb01d8f828a6c9a20be4534e72e049aaf41503df@scylladb.com>
Closes #853

cloudius-systems/seastar,avikivity/seastar,avikivity/seastar,avikivity/seastar,scylladb/seastar,cloudius-systems/seastar,scylladb/seastar,syuu1228/seastar,syuu1228/seastar,cloudius-systems/seastar,syuu1228/seastar,scylladb/seastar