app/testpmd: fix device mcast list error handling

app/testpmd: fix device mcast list error handling

The multicast set list function now has a return value, which is checked
by the calling functions. A rollback occurs on detection of failure, to
realign local config with the device config.

The error print statement in the function had included the port_id and
mc_addr_nb values in the wrong order, these are now swapped.

Fixes: 8fff667578a7 ("app/testpmd: new command to add/remove multicast MAC addresses")
Cc: stable@dpdk.org
Signed-off-by: Ciara Power <ciara.power@intel.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>