netd: Support the Qualcomm SoftAP SDK.

The Qualcomm SoftAP SDK extendes the HotSpot capability provided by
the stock Android distribution.  This allows the creation of a more
feature-rich HotSpot application.

In order to minimize the changes required to the stock Android
distribution, place the majority of the changes into a new
QualcommSoftapCmd class that contains most of the command dispatching
logic.
(cherry picked from commit fe80af085ac7a46243b923a617619d5f6fe5b0cd)

Change-Id: I866934c446b8fc2a670a445c7e425e0948956bf7