Add start/stop-softap shell command

Add start-softap and stop-softap wifi shell commands to help automate
wifi hotspot tests. Note that this doesn't go through tetheringManager.
In some devices, internet sharing might be possible if wifi STA is also
enabled and is associated to another AP with internet access.

Bug: 155682782
Test: atest com.android.server.wifi.WifiShellCommandTest
Test: manual test with "adb shell cmd wifi start/stop-softap" in open/wpa2
modes with different band options. In all tested modes, another device can
associate to the DUT's hotspot. If DUT's STA is also enabled and associated
to another internet-bounding AP, internet should be also avaiable to the
device associated to DUT's hotspot.

Change-Id: I9ad561b0e10171ff9ccb395e1538472ac637e17a
2 files changed