nimble/host: Fix assert when registering GATT server characteristics

If CEP is used, but no CCD than expected handle may vary. Instead of
hardcoded value use variable for tracking expected next handle.

Author: sjanc

nimble/host/src/ble_gatts.c

@@ -904,6 +904,7 @@ ble_gatts_register_chr(const struct ble_gatt_svc_def *svc,
     uint16_t val_handle;
     uint16_t dsc_handle;
     uint16_t cep_handle;
+    uint16_t expected_handle;
     uint8_t att_flags;
     int rc;
 
@@ -927,6 +928,9 @@ ble_gatts_register_chr(const struct ble_gatt_svc_def *svc,
         return rc;
     }
 
+    expected_handle = def_handle;
+    (void)expected_handle;
+
     /* Register characteristic value attribute (cast away const on callback
      * arg).
      */
@@ -937,7 +941,7 @@ ble_gatts_register_chr(const struct ble_gatt_svc_def *svc,
     if (rc != 0) {
         return rc;
     }
-    BLE_HS_DBG_ASSERT(val_handle == def_handle + 1);
+    BLE_HS_DBG_ASSERT(val_handle == ++expected_handle);
 
     if (chr->val_handle != NULL) {
         *chr->val_handle = val_handle;
@@ -957,15 +961,15 @@ ble_gatts_register_chr(const struct ble_gatt_svc_def *svc,
         if (rc != 0) {
             return rc;
         }
-        BLE_HS_DBG_ASSERT(dsc_handle == def_handle + 2);
+        BLE_HS_DBG_ASSERT(dsc_handle == ++expected_handle);
     }
 
     if (ble_gatts_chr_ext_prop_allowed(chr) != 0) {
         rc = ble_gatts_register_cep_dsc(&cep_handle, chr->flags);
         if (rc != 0) {
             return rc;
         }
-        BLE_HS_DBG_ASSERT(cep_handle == def_handle + 3);
+        BLE_HS_DBG_ASSERT(cep_handle == ++expected_handle);
     }
 
     /* Register each descriptor. */