app/testpmd: fix DCB set

app/testpmd: fix DCB set

When set DCB in testpmd, there is a segmentation fault. It is
because the local variable rss_conf in get_eth_dcb_conf()
is not cleared, so that the pointer member variable rss_key has
a random address, which leads to an error in the following
processing. This patch initialized the local variable rss_conf
to avoid this situation.

Fixes: ac7c491c3fec ("app/testpmd: fix DCB config")
Cc: stable@dpdk.org
Signed-off-by: Ting Xu <ting.xu@intel.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>