[vty] Separate BSC and MSC statistics. Make it easy to print them.

Move the statistics command into the MSC part and move the
BSC statistics printing into a subroutine.
diff --git a/openbsc/include/openbsc/vty.h b/openbsc/include/openbsc/vty.h
index 40e2191..f1b1148 100644
--- a/openbsc/include/openbsc/vty.h
+++ b/openbsc/include/openbsc/vty.h
@@ -1,6 +1,10 @@
 #ifndef OPENBSC_VTY_H
 #define OPENBSC_VTY_H
 
+struct gsm_network;
+struct vty;
+
 void openbsc_vty_add_cmds(void);
+void openbsc_vty_print_statistics(struct vty *vty, struct gsm_network *);
 
 #endif