fix portability: add min() macro

Add min() macro definition to improve portability.

Author: manuelinbrain

nimble/controller/src/ble_ll_ctrl.c

@@ -34,6 +34,10 @@
 #include "controller/ble_ll_tmr.h"
 #include "ble_ll_conn_priv.h"
 
+#ifndef min
+#define min(a, b) ((a) < (b) ? (a) : (b))
+#endif
+
 #if MYNEWT_VAL(BLE_LL_ROLE_PERIPHERAL) || MYNEWT_VAL(BLE_LL_ROLE_CENTRAL)
 
 /* To use spec sample data for testing */