[vty] In case of handover only warn about the proxy mode when it is enabled

Do not warn if the user has put "handover 0" in his configuration
as this will not enable handover, only warn if it is going to be
enabled.
diff --git a/openbsc/src/vty_interface.c b/openbsc/src/vty_interface.c
index f978c27..8d6e202 100644
--- a/openbsc/src/vty_interface.c
+++ b/openbsc/src/vty_interface.c
@@ -1212,13 +1212,15 @@
       "handover (0|1)",
 	"Whether or not to use in-call handover")
 {
-	if (ipacc_rtp_direct) {
+	int enable = atoi(argv[0]);
+
+	if (enable && ipacc_rtp_direct) {
 		vty_out(vty, "%% Cannot enable handover unless RTP Proxy mode "
 			"is enabled by using the -P command line option%s",
 			VTY_NEWLINE);
 		return CMD_WARNING;
 	}
-	gsmnet->handover.active = atoi(argv[0]);
+	gsmnet->handover.active = enable;
 
 	return CMD_SUCCESS;
 }