app/testpmd: fix empty list of RSS queues for flow

app/testpmd: fix empty list of RSS queues for flow

Since the commit referenced below, specifying a RSS action without any
queues (e.g. "actions rss queues end / end") does not override the default
set automatically generated by testpmd.

In short, one cannot instantiate a RSS action with 0 target queues anymore
in order to determine how PMDs react (hint: this is currently undocumented
so they may reject it, however ideally they should interpret it as a
default setting like for other fields where empty values stand for
"defaults".)

Fixes: d0ad8648b1c5 ("app/testpmd: fix RSS flow action configuration")
Cc: stable@dpdk.org
Signed-off-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>