timer: Fix compiler warning about timeval

timer.c:27:23: warning: tentative definition of variable with internal linkage has incomplete
      non-array type 'struct timeval' [-Wtentative-definition-incomplete-type]
static struct timeval nearest;
                      ^
timer.c:27:15: note: forward declaration of 'struct timeval'
static struct timeval nearest;
diff --git a/src/timer.c b/src/timer.c
index c8376c8..21b7015 100644
--- a/src/timer.c
+++ b/src/timer.c
@@ -23,9 +23,6 @@
  *
  */
 
-/* These store the amount of time that we wait until next timer expires. */
-static struct timeval nearest;
-static struct timeval *nearest_p;
 
 /*! \addtogroup timer
  *  @{
@@ -41,6 +38,10 @@
 #include <osmocom/core/timer_compat.h>
 #include <osmocom/core/linuxlist.h>
 
+/* These store the amount of time that we wait until next timer expires. */
+static struct timeval nearest;
+static struct timeval *nearest_p;
+
 static struct rb_root timer_root = RB_ROOT;
 
 static void __add_timer(struct osmo_timer_list *timer)