Relax protected broadcast checks for shell.

On userdebug/eng devices, the shell can run as non-shell UIDs, so
define a flag to identify broadcasts coming from the shell, and
don't yell if they're non-protected.

Test: builds, boots, root shell can send broadcasts
Bug: 32369665
Change-Id: I5f55930ee434cb8318c86aaf05eba3c59a326694