manager: make sure we don't reset the modem twice in a row

This patch adds a 3s delay when resetting the modem during which we 
avoid triggering a new reset. This makes sure we don't trigger a reset 
twice in a row.

It also disables any related running timer to avoid being re-triggered 
unnecessarily.

src/suspend.c

@@ -20,6 +20,7 @@
 static gboolean check_modem_resume(struct EG25Manager *manager)
 {
     g_message("Modem wasn't probed in time, restart it!");
+    manager->suspend_source = 0;
     modem_reset(manager);
 
     return FALSE;