llkd: requires sys_admin permissions

As a result of commit f8a00cef17206ecd1b30d3d9f99e10d9fa707aa7
("proc: restrict kernel stack dumps to root")
the userdebug feature where llkd can monitor for live lock
signatures in the stack traces broke.

So now userdebug variant of llkd requires sys_admin permissions.

Signed-off-by: Mark Salyzyn <salyzyn@google.com>
Test: llkd_unit_test
Bug: 147486902
Change-Id: I31572afa08daa490a69783855bce55313eaed96c