Directly call 'ctl.restart' on adbd if adb is enabled

Rather than disabling adb and relying on the settings ContentObserver to
take care of re-enabling adb, just kick adbd ourselves directly. Relying
on the ContentObserver appears to cause a race condition on some
devices.

Test: manual, run adb shell cmd testharness enable on a userdebug device
Bug: 170327166
Change-Id: I204857c14251a60886b7023ada717812cbf70c59