Fix hotword module constantly restarting on Pixel 2.

|hotwordEnabled| is in the advanced constraints vector becuase it's an
optional constraint.

BUG=583720
TEST=Manually tested "Ok Google" on Pixel 2.

Review URL: https://codereview.chromium.org/1725213002

Cr-Commit-Position: refs/heads/master@{#378177}
1 file changed