zebra: print "no link-detect"

The default for this is slated to change, so let's print the current
default value for preexisting configurations.

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
diff --git a/zebra/interface.c b/zebra/interface.c
index 7e1d3dd..0271061 100644
--- a/zebra/interface.c
+++ b/zebra/interface.c
@@ -1579,6 +1579,8 @@
 
       if (CHECK_FLAG(ifp->status, ZEBRA_INTERFACE_LINKDETECTION))
 	vty_out(vty, " link-detect%s", VTY_NEWLINE);
+      else
+	vty_out(vty, " no link-detect%s", VTY_NEWLINE);
 
       for (ALL_LIST_ELEMENTS_RO (ifp->connected, addrnode, ifc))
 	  {