Add a menu to the installer to run fwget(8) inside the newly installed
system to install firmware known to be needed.
This requires working netowrking.
This is needed ate least for wireless currently for when we entirely
stop shipping new firmware in src.git to have working networking on
the installed system (we already do need this for at least rtw89).
While here make sure an interface is back up before (re-)starting
wpa_supplicant in wlanconfig not relying on wpa to UP the interface
(though we fixed that).
Sponsored by: The FreeBSD Foundation
Tested with: four different iwlwifi chipsets in a system
MFC after: 3 days