hostapd: Add multi_ap settings to get_config() output

hostapd: Add multi_ap settings to get_config() output

Since a running hostapd is not necessarily using the settings that are
in the configuration file (if they were changed at runtime, or the file
was changed but not reloaded, etc.), being able to get their value at
runtime can be useful (to know if they have to be updated for example).

If multi_ap is set, also print the SSID and passphrase (or PSK).

Signed-off-by: Raphaël Mélotte <raphael.melotte@mind.be>