am: Allow more hidden apps on devices with lots of RAM

 * If more than 1.5GB is present, allow up to 40 hidden apps.
 * Number is somewhat arbitrary, but was found to work well on D2.
 * Also look at the sys.mem.max_hidden_apps value if given.

Change-Id: I2d3cf6e0dad1bc0b482cc37bf9c61ed2f2b4be51
Wifi: Enable Ad-Hoc (IBSS) network configuration

This adds two public but hidden variables to WifiConfiguration: isIBSS and
frequency. These are used for configuring IBSS mode.

WifiConfigStore is exended to get and set these variables to wpa_supplicant
(via WifiNative).

Change-Id: Iab02c3d738c05c2de036350ea77b78789213e357
Wifi: Add IBSS supported method

Add method isIbssSupported() to WifiManager and related classes to query wether
the driver supports IBSS mode. The query is answered by wpa_supplicants new
command "get_capability modes".

It will only return a correct result after WIFI_STATE_ENABLED has been
reached.

Change-Id: I93aa2fdff94cd897c91ec3beb7e58940d1de7b72