router: use explicit args in API calls

Currently, internal router API functions use varargs to pass arguments.
This differs from the storage API implementation, where arguments are
explicit.

This patch replaces varargs with explicit arguments in the
router_api_call_safe, router_api_call_unsafe and router_make_api
functions.

Motivation:
- Consistency between router and storage internal APIs
- Using explicit arguments instead of varargs is more
  friendly to the JIT compiler

Part of #266

NO_DOC=refactoring
NO_TEST=refactoring

Author: kamenkremen

vshard/router/init.lua

@@ -1661,15 +1661,16 @@ end
 -- Public API protection
 --------------------------------------------------------------------------------
 
-local function router_api_call_safe(func, router, ...)
-    return func(router, ...)
+local function router_api_call_safe(func, router, arg1, arg2, arg3, arg4, arg5)
+    return func(router, arg1, arg2, arg3, arg4, arg5)
 end
 
 --
 -- Unsafe proxy is loaded with protections. But it is used rarely and only in
 -- the beginning of instance's lifetime.
 --
-local function router_api_call_unsafe(func, router, ...)
+local function router_api_call_unsafe(func, router, arg1, arg2,
+                                      arg3, arg4, arg5)
     -- Router can be started on instance with unconfigured box.cfg.
     if not router.is_configured then
         local msg = 'router is not configured'
@@ -1680,12 +1681,12 @@ local function router_api_call_unsafe(func, router, ...)
         return error(lerror.vshard(lerror.code.ROUTER_IS_DISABLED, msg))
     end
     router.api_call_cache = router_api_call_safe
-    return func(router, ...)
+    return func(router, arg1, arg2, arg3, arg4, arg5)
 end
 
 local function router_make_api(func)
-    return function(router, ...)
-        return router.api_call_cache(func, router, ...)
+    return function(router, arg1, arg2, arg3, arg4, arg5)
+        return router.api_call_cache(func, router, arg1, arg2, arg3, arg4, arg5)
     end
 end