Swap param order in registerSoftApCallback

Moving executor to be the first argument in registerSoftApCallback.

Bug: 144379300
Test: atest FrameworksWifiApiTests:android.net.wifi.WifiManagerTest
Manually on pixel 3

Change-Id: I7074278d16beac422ce7b29d4471b2794fa97825
Merged-In: I7074278d16beac422ce7b29d4471b2794fa97825