Revert "zebra: Set link-detect on by default"

This reverts commit 773224404cb33b2dbd3d8d8d2572013603995ce4.

This patch is nontrivial but wasn't passed along on the mailing list;
this is a revert purely on procedural reasons.

Signed-off-by: David Lamparter <equinox@diac24.net>
diff --git a/lib/if.c b/lib/if.c
index 2b46a1b..3a1f9b4 100644
--- a/lib/if.c
+++ b/lib/if.c
@@ -132,9 +132,6 @@
   ifp->connected = list_new ();
   ifp->connected->del = (void (*) (void *)) connected_free;
 
-  /* Enable Link-detection by default */
-  SET_FLAG(ifp->status, ZEBRA_INTERFACE_LINKDETECTION);
-
   if (if_master.if_new_hook)
     (*if_master.if_new_hook) (ifp);