test: gprs_ns2: don't leak the talloc context

Makes the address sanitizer happy

Change-Id: Ibf926d8db88cdb403d29de5e666dfb71eefc7b72
diff --git a/tests/gb/gprs_ns2_test.c b/tests/gb/gprs_ns2_test.c
index 86a0190..d53dc88 100644
--- a/tests/gb/gprs_ns2_test.c
+++ b/tests/gb/gprs_ns2_test.c
@@ -160,5 +160,6 @@
 	test_nse_transfer_cap(ctx);
 	printf("===== NS2 protocol test END\n\n");
 
+	talloc_free(ctx);
 	exit(EXIT_SUCCESS);
 }