flimflam: add "psk" security as a way to specify either "wpa" or "rsn"

doc/service-api.txt

 Service hierarchy
 =================
 
 Service         org.chromium.flimflam
 Interface       org.chromium.flimflam.Service
 Object path     [variable prefix]/{service0,service1,...}
 
 Methods         dict GetProperties()
 
                         Returns properties for the service object. See
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                         This property is present only for WiFi services.
 
                 string Security [readonly]
 
                         If the service type is "wifi", then this property is
                         present and contains the security method or key
                         management setting.
 
                         Possible values are: "none" (no privacy),
                         "wep" (fixed key WEP), "wpa" (WPA-PSK), "rsn"
-                        (IEEE 802.11i-PSK), and "802_1x" (IEEE 802.11i
-                        with 802.1x authentication).
+                        (IEEE 802.11i-PSK), "psk" (either "wpa" or "rsn"),
+                        and "802_1x" (IEEE 802.11i with 802.1x authentication).
 
                         This property is only present for WiFi services.
 
                 string Passphrase [readwrite]
 
                         If the service type is "wifi", then this property
                         holds a passphrase used in setting up services of
                         type "wep", "wpa", and "rsn", or a private
                         key password used in setting up services of
                         type "802_1x".
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                         the READY state.
 
                         string Domain [readonly]
                                 VPN domain name.
                         string Host [readonly]
                                 VPN host IP address.
                         string Name [readonly]
                                 VPN provider name.
                         string Type [readonly]
                                 VPN provider type (e.g. openvpn).