fix strncpy() invocation in vty_interface_layer3.c and 3 tests

Use osmo_strlcpy() to fix unsafe invocation of strncpy(), which potentially
left the result unterminated.

Change-Id: I1a119b1760a3e3262538b4b012d476fdce505482
diff --git a/openbsc/tests/mgcp/mgcp_test.c b/openbsc/tests/mgcp/mgcp_test.c
index e2dc8fa..b2d237e 100644
--- a/openbsc/tests/mgcp/mgcp_test.c
+++ b/openbsc/tests/mgcp/mgcp_test.c
@@ -25,6 +25,7 @@
 
 #include <osmocom/core/application.h>
 #include <osmocom/core/talloc.h>
+#include <osmocom/core/utils.h>
 #include <string.h>
 #include <limits.h>
 #include <dlfcn.h>
@@ -54,7 +55,7 @@
 	char buf[2048];
 	int counter = 0;
 
-	strncpy(buf, strline_test_data, sizeof(buf));
+	osmo_strlcpy(buf, strline_test_data, sizeof(buf));
 
 	for (line = strline_r(buf, &save); line;
 	     line = strline_r(NULL, &save)) {