host/mesh: define Low Latency mode for non-NimBLE controller

This fixes build for porting

nimble/host/mesh/src/adv_legacy.c

@@ -22,6 +22,12 @@
 /* Convert from ms to 0.625ms units */
 #define ADV_SCAN_UNIT(_ms) ((_ms) * 8 / 5)
 
+#if (MYNEWT_VAL(BSP_NRF51) && !MYNEWT_VAL(BLE_CONTROLLER))
+#define CONFIG_BT_CTLR_LOW_LAT 1
+#else
+#define CONFIG_BT_CTLR_LOW_LAT 0
+#endif
+
 /* Pre-5.0 controllers enforce a minimum interval of 100ms
  * whereas 5.0+ controllers can go down to 20ms.
  */
@@ -83,7 +89,7 @@ static inline void adv_send(struct os_mbuf *buf)
 	 * amount of scan window duration to compensate for the blocked
 	 * advertising events.
 	 */
-	if (MYNEWT_VAL(BSP_NRF51)) {
+	if (CONFIG_BT_CTLR_LOW_LAT) {
 		duration += BT_MESH_SCAN_WINDOW_MS;
 	}
 #endif

porting/examples/linux_blemesh/include/syscfg/syscfg.h

@@ -1013,6 +1013,11 @@
 #define MYNEWT_VAL_BLE_MESH_OOB_OUTPUT_SIZE (4)
 #endif
 
+
+#ifndef MYNEWT_VAL_BSP_NRF51
+#define MYNEWT_VAL_BSP_NRF51 (0)
+#endif
+
 /* Overridden by @apache-mynewt-nimble/porting/targets/linux_blemesh (defined by @apache-mynewt-nimble/nimble/host/mesh) */
 #ifndef MYNEWT_VAL_BLE_MESH_PB_ADV
 #define MYNEWT_VAL_BLE_MESH_PB_ADV (1)