Disable periodic interface re-scans on modern platforms

This commit disables periodic interface re-scans timer on Linux where
a kernel-based dynamic interface mechanisms make it a thing of the
past in most cases.

lib/ns/include/ns/interfacemgr.h

@@ -190,3 +190,11 @@ ns_interfacemgr_getclientmgr(ns_interfacemgr_t *mgr);
  * Returns the client manager for the current worker thread.
  * (This cannot be run from outside a network manager thread.)
  */
+
+bool
+ns_interfacemgr_dynamic_updates_are_reliable(void);
+/*%<
+ * Returns 'true' if periodic interface re-scans timer should be
+ * disabled. That is the case on the platforms where kernel-based
+ * mechanisms for tracking networking interface states is reliable enough.
+ */

lib/ns/interfacemgr.c

@@ -1379,3 +1379,17 @@ ns_interfacemgr_getclientmgr(ns_interfacemgr_t *mgr) {
 
 	return (mgr->clientmgrs[tid]);
 }
+
+bool
+ns_interfacemgr_dynamic_updates_are_reliable(void) {
+#if defined(LINUX_NETLINK_AVAILABLE)
+	/*
+	 * Let's disable periodic interface rescans on Linux, as there a
+	 * reliable kernel-based mechanism for tracking interface state
+	 * changes is available.
+	 */
+	return (true);
+#else
+	return (false);
+#endif /* LINUX_NETLINK_AVAILABLE */
+}