v1.8.4: leave single-adapter roaming to NetworkManager

Fixed

• With fewer than two available Wi-Fi radios, leave roaming and DHCP to
  NetworkManager. Previously, leaving Multipath on let the planner disconnect
  the sole radio after a short gateway-ping gap or signal dip, then cancel its
  replacement connection after 15 seconds without an address. Restore temporary
  profile settings and autoconnect holds without dropping the link; discard old
  joins, AP bans and failsafe timers before resuming with a second radio.
• Retry failed temporary-profile restorations as well as failed autoconnect
  releases when handing control back to NetworkManager.

Full change: #7