[spp] Failed to init ring_latency_stats_info

[Yasufumi Ogawa <yasufum.o@gmail.com>]

Hi Hideyuki,

I have a problem in initializing SPP ringlatencystats. rte_zmalloc() in 
spp_ringlatencystats_init() returns NULL and process is terminated with 
log as below.

...
SPP_RING_LATENCY_STATS: Cannot allocate memory for ring latency stats info
SPP_VF: Exit spp_vf

I made some changes to this file for refactoring, but it might not 
related to the error from `git blame`. It is simply calling 
rte_zmalloc() with sizeof() and I cannot understand why error is happened.

spp_ringlatencystats_init(uint64_t samp_intvl, uint16_t stats_count)
{
	/* allocate memory for ring latency statistics information */
	g_stats_info = rte_zmalloc(
			"global ring_latency_stats_info",
			sizeof(struct ring_latency_stats_info) * stats_count,
			0);
	if (unlikely(g_stats_info == NULL)) {
		RTE_LOG(ERR, SPP_RING_LATENCY_STATS, "Cannot allocate memory "
				"for ring latency stats info\n");
		return SPPWK_RET_NG;
	}

Although ringlatencystats is not activated by default and almost no one 
use, it should be fixed.

Thanks,
Yasufumi