clatd: implement seccomp system call protection

but only enable it in enforcing mode on aarch64,
since that gets good test coverage via Pixel
on GoogleGuest ipv6-only wifi network
and (for example) T-Mobile US cellular.

For other architectures this will only result
in (automatically ratelimitted to at most 5/s)
audit logs for any 'unusual' system calls.

Test: TreeHugger, manually on Pixel on GoogleGuest wifi
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: Id14c6d9db8d7b4652c7358cac101a82ef09843e0
2 files changed