Slow wifi-reconnection when waking up

[Stefan Monnier <monnier@iro.umontreal.ca>]

When I wake up from suspend, my Debian machines take a "long" time to
reconnect to the wifi.  Looking at the `nm-applet` icon in my XFCE4
panel, I see:
- for about 10s the icon is "two computers" (which IIUC represents
  just NetworkManager).
- then the icon changes to the one representing a wired ethernet
  connection and stays that way for about 10s (there's nothing
  plugged into the ethernet port of this computer).
- then the icon changes to the "two dots, with something circling
  between them" which indicates that the system is in the process of
  connecting to a wifi network.
- after about 5s this changes to the bars representation of the
  signal quality.

IOW, while it takes about 5s to connect to the wifi network, it takes
about 20 additional seconds for NM to decide that it should try to
connect.

I have the impression that a few years ago, my Debian machines
reconnected more quickly to the wifi.

I can live with this delay, especially when it's waking up in
a different place than where it got suspended, but in the case where
it's waking up at the same place where it got suspended, those extra 20s
seem hard to justify.

Any idea what might be going on and how to make it quicker?


        Stefan