Fix missing #include preventing compilation of vty_interface.c
diff --git a/openbsc/src/vty_interface.c b/openbsc/src/vty_interface.c
index 70d2997..8661316 100644
--- a/openbsc/src/vty_interface.c
+++ b/openbsc/src/vty_interface.c
@@ -39,6 +39,7 @@
 #include <osmocore/talloc.h>
 #include <openbsc/telnet_interface.h>
 #include <openbsc/vty.h>
+#include <openbsc/gprs_ns.h>
 
 static struct gsm_network *gsmnet;