nimble/host: Restore key size for LTK

When LTK is restored successfully we also need to update key size for
proc with proper value as otherwise we default to 0 which means that
e.g. any characteristic which requires proper key size for read/write
cannot be accessed.

nimble/host/src/ble_sm.c

@@ -1306,6 +1306,7 @@ ble_sm_ltk_restore_exec(struct ble_sm_proc *proc, struct ble_sm_result *res,
             proc->conn_handle, value_sec->ltk);
 
         if (res->app_status == 0) {
+            proc->key_size = value_sec->key_size;
             if (value_sec->authenticated) {
                 proc->flags |= BLE_SM_PROC_F_AUTHENTICATED;
             }