Fix bridge disconnect icon and add OvsBridge support

BUG: 517384

Bug: Pulling the cable from a bridge slave port left the tray icon stuck on network-wired-activated, because NetworkManager keeps the bridge connection active even after physical link loss. The old code unconditionally set the activated icon for bridge devices. Fix and additions:

• Bridge: now checks hasEthernetCarrier() before deciding the icon. If no Ethernet device has carrier, falls back to setDisconnectedIcon() which shows the correct disconnected/available/unavailable icon.
• OvsBridge: new handler for NetworkManager::Device::OvsBridge with the same carrier-aware logic. Previously OVS bridges always fell through to the else branch and always showed the disconnected icon.
• hasEthernetCarrier(): extracted as a private const method on ConnectionIcon, reused by Bridge, OvsBridge.