app/testpmd: fix --stats-period option check

[ upstream commit 2ae06c579ea4e1cd234c5b14bef2957ee154ec74 ]

Rather than silently ignore an invalid value, raise an error for
stats-period user input.

Fixes: cfea1f3 ("app/testpmd: print statistics periodically")

Signed-off-by: David Marchand <david.marchand@redhat.com>
Acked-by: Ferruh Yigit <ferruh.yigit@amd.com>

app/test-pmd/parameters.c

@@ -763,7 +763,7 @@ launch_args_parse(int argc, char** argv)
 				n = strtoul(optarg, &end, 10);
 				if ((optarg[0] == '\0') || (end == NULL) ||
 						(*end != '\0'))
-					break;
+					rte_exit(EXIT_FAILURE, "Invalid stats-period value\n");
 
 				stats_period = n;
 				break;