Check user volume adjustment restrictions only once.

Perform volume restriction check only on dialog opening. Before this
 change the check was performed upon rendering every item in the
 device list which is unnecessary.

Bug: 414668703
Flag: com.android.media.flags.avoid_binder_calls_during_render
Test: atest MediaSwitchingControllerTest, on a device.
Change-Id: I75463830cb842cd1b0d132382b731f28150bd9ca