dpdk-stub: Change the ERR log to DBG.

When DPDK is not availble and avx512 looks for isa
the function returns an error log which results in
unit test failures.

By logging a debug level log, this still shows up
in the vswitchd.log file, but won't fail unit tests
that do not have DPDK built in.

Suggested by: Ilya Maximets <i.maximets@ovn.org>
Signed-off-by: Kumar Amber <kumar.amber@intel.com>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>

lib/dpdk-stub.c

@@ -83,7 +83,7 @@ bool
 dpdk_get_cpu_has_isa(const char *arch OVS_UNUSED,
                      const char *feature OVS_UNUSED)
 {
-    VLOG_ERR_ONCE("DPDK not supported in this version of Open vSwitch, "
+    VLOG_DBG_ONCE("DPDK not supported in this version of Open vSwitch, "
                   "cannot use CPU flag based optimizations");
     return false;
 }