interfaces: prefer GUAs over ULAs when returning addresses

The concept is a bit convoluted, but apparently better than
ignoring the fact that a ULA cannot replace a GUA ever.

PR: https://forum.opnsense.org/index.php?topic=36893.0

src/etc/inc/interfaces.inc

@@ -4357,6 +4357,7 @@ function interfaces_addresses($interfaces, $as_subnet = false, $ifconfig_details
                     'key' => $key,
                     'name' => $realif,
                     'scope' => !empty($address['link-local']),
+                    'unique' => ($proto == 'ipv4' || !empty($address['link-local'])) ? false : is_uniquelocal($address['ipaddr']),
                 ];
             }
         }
@@ -4397,6 +4398,11 @@ function interfaces_addresses($interfaces, $as_subnet = false, $ifconfig_details
         }
     }
 
+    /* move ULAs to the bottom to prefer GUA addresses */
+    usort($result, function ($a, $b) {
+        return $a['unique'] - $b['unique'];
+    });
+
     return $result;
 }
 
@@ -4462,7 +4468,7 @@ function _interfaces_primary_address6($interface, $ifconfig_details = null, $all
 
         if ($link_local && !$addr['scope']) {
             continue;
-        } elseif (!$link_local && ($addr['scope'] || is_uniquelocal($addr['address']))) {
+        } elseif (!$link_local && $addr['scope']) {
             continue;
         }