Explicitly restart the killed wallpaper service

Symptom:
Live wallpaper setting was reset when a wallpaper service was killed
by Lmk. The wallpaper fell back to the default image wallpaper. It's
a black bitmap.

Root cause:
When restarting wallpaper service takes more than 10 seconds, it's
treated as a bad wallpaper. The wallpaper setting is reset to remove
the bad wallpaper.

This is not a suitable solution under the low memory situation.
Multiple processes are killed by Lmk at one time. Killed services are
automatically restarted by AMS with a few seconds interval.
The restart interval is increased by a factor of the number of killed
services. Sometimes, it takes more than 1 minute.

Solution:
When a wallpaper service is killed, WallpaperManagerService requests
restarting the service immediately. It can ignore the restart interval.

Bug: 73071020
Change-Id: Id5bb1cf121029a513f8773597f296b47667d1e21