Don't show warning dialog on opening ASM settings.

On older devices, the activation warning dialog would show upon the
switchbar changing to On. This was occurring when the page opens
because the status was changing onResume. By shuffling the switchbar
changes into the ASMSwitchBarController, we can register our listener
after the initialization of the switch bar's first status.

Change-Id: I3610d07345684d1e66444981a8059d1c2965e955
Fixes: 37472724
Test: Settings robotests