env: define mempool/memzone name length limits

DPDK memzone name limit is 32 and mempool's 29 as it
internally reserves a memzone with "MP_" prefix.

DPDK also offers defines for those limits, but we
obviously can't use them in generic env header file.

Change-Id: I16abcf404eee390a9033135e996cba1716baca5f
Signed-off-by: Dariusz Stojaczyk <dariuszx.stojaczyk@intel.com>
Reviewed-on: https://review.gerrithub.io/416979
Tested-by: SPDK Automated Test System <sys_sgsw@intel.com>
Reviewed-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>

include/spdk/env.h

@@ -58,6 +58,9 @@ extern "C" {
  */
 #define SPDK_MALLOC_SHARE  0x02
 
+#define SPDK_MAX_MEMZONE_NAME_LEN 32
+#define SPDK_MAX_MEMPOOL_NAME_LEN 29
+
 /**
  * Memzone flags
  */