Fix conf_overwrite filter removing vlan mgmt entries

The vlan/mgmt lookahead split (commit dcc60c3) correctly separated the
patterns so that `vlan N mgmt` and `vlan N <members>` match different
conf_overwrite entries. But the filter that applies the overwrite still
used `item.startsWith(matchStr + " ")` with matchStr = "vlan N", which
also matches "vlan N mgmt" — so the management entry was removed whenever
the VLAN's membership definition was re-saved.

Example: with both `vlan 44 management 2t 4t 5 6t` and `vlan 44 mgmt`
in the config, changing the membership dropped `vlan 44 mgmt` entirely.

Added a `!item.endsWith(" mgmt")` guard so management entries survive the
filter. No reordering is needed: `vlan N mgmt` only sets the global
management_vlan variable (cmd_parser.c) and does not depend on the VLAN
table entry existing, so its position in the config is irrelevant.

html/config.js

@@ -71,7 +71,7 @@ function parseConf(s){
         let m = line.match(x);
         let matchStr = m[0];
         configuration = configuration.filter(item =>
-          !(item === matchStr || item.startsWith(matchStr + " ")));
+          !(item === matchStr || (item.startsWith(matchStr + " ") && !item.endsWith(" mgmt"))));
         break;
       }
     }