mtpd: whitelist 'nanosleep' syscall in seccomp-bpf filter

BUG=chromium:693673
TEST=Verified that mtpd runs properly on different platforms.

Change-Id: Ifb59fa0f1aa5c0fd23c9b2b7aa4c1d2102336092
Reviewed-on: https://chromium-review.googlesource.com/444035
Commit-Ready: Ben Chan <benchan@chromium.org>
Tested-by: Ben Chan <benchan@chromium.org>
Reviewed-by: Jorge Lucangeli Obes <jorgelo@chromium.org>
diff --git a/mtpd-seccomp-amd64.policy b/mtpd-seccomp-amd64.policy
index fa99e66..3da830b 100644
--- a/mtpd-seccomp-amd64.policy
+++ b/mtpd-seccomp-amd64.policy
@@ -67,3 +67,4 @@
 prctl: arg0 == 0xf
 setpriority: 1
 getrandom: 1
+nanosleep: 1
diff --git a/mtpd-seccomp-arm.policy b/mtpd-seccomp-arm.policy
index a1e4487..a26920a 100644
--- a/mtpd-seccomp-arm.policy
+++ b/mtpd-seccomp-arm.policy
@@ -69,3 +69,4 @@
 prctl: arg0 == 0xf
 setpriority: 1
 getrandom: 1
+nanosleep: 1
diff --git a/mtpd-seccomp-x86.policy b/mtpd-seccomp-x86.policy
index 3a00b6a..fd0e751 100644
--- a/mtpd-seccomp-x86.policy
+++ b/mtpd-seccomp-x86.policy
@@ -63,3 +63,4 @@
 prctl: arg0 == 0xf
 setpriority: 1
 getrandom: 1
+nanosleep: 1