main: Add missing #include to osmocom/timer.h

Change-Id: I9a062fbe9e0f25e45e9321048d8cbdecd4c49076
diff --git a/sysmoOCTSIM/main.c b/sysmoOCTSIM/main.c
index 6e2d6ac..15e2004 100644
--- a/sysmoOCTSIM/main.c
+++ b/sysmoOCTSIM/main.c
@@ -24,6 +24,7 @@
 #include <errno.h>
 
 #include <osmocom/core/utils.h>
+#include <osmocom/core/timer.h>
 
 #include <hal_cache.h>
 #include <hri_port_e54.h>