Port gbproxy to NS2

Since NS2 has a different abstraction we mock up the prim send/recv
functions and don't test NS like the old tests did.

Related: SYS#4998
Change-Id: Iecfd0408a35a11638d254c1db3c1d477b1a11524
diff --git a/src/gb_proxy_patch.c b/src/gb_proxy_patch.c
index 2bc3b4b..9c70d3f 100644
--- a/src/gb_proxy_patch.c
+++ b/src/gb_proxy_patch.c
@@ -18,6 +18,7 @@
  *
  */
 
+#include <osmocom/gprs/gprs_msgb.h>
 #include <osmocom/sgsn/gb_proxy.h>
 
 #include <osmocom/sgsn/gprs_utils.h>