Update bgp filters : fix the parameter name

etc/local/bird/bird/bgp.conf

@@ -8,7 +8,7 @@
 #
 template bgp tpl_bgp {
         # Use MED for routes received by different ASes
-        bgp med;
+        med metric;
 }
 
 

etc/local/bird/bird6/bgp.conf

@@ -7,7 +7,7 @@
 #
 template bgp tpl_bgp {
         # Use MED for routes received by different ASes
-        bgp med;
+        med metric;
 }